Analyte Sensors Having a Membrane with Low Temperature Sensitivity

ABSTRACT

Embodiments of the present disclosure relate to analyte determining methods and devices (e.g., electrochemical analyte monitoring systems) that have a membrane with low temperature sensitivity. The sensing layer is disposed on a working electrode of in vivo and/or in vitro analyte sensors, e.g., continuous and/or automatic in vivo monitoring using analyte sensors and/or test strips. Also provided are systems and methods of using the, for example electrochemical, analyte sensors in analyte monitoring.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. §119(e), this application claims priority to U.S.Provisional Patent Application No. 61/488,546 filed on May 20, 2011, thedisclosure of which is herein incorporated by reference in its entirety.

INTRODUCTION

In many instances it is desirable or necessary to regularly monitor theconcentration of particular constituents in a fluid. A number of systemsare available that analyze the constituents of bodily fluids such asblood, urine and saliva. Examples of such systems conveniently monitorthe level of particular medically significant fluid constituents, suchas, for example, cholesterol, ketones, vitamins, proteins, and variousmetabolites or blood sugars, such as glucose. Diagnosis and managementof patients suffering from diabetes mellitus, a disorder of the pancreaswhere insufficient production of insulin prevents normal regulation ofblood sugar levels, requires carefully monitoring of blood glucoselevels on a daily basis. A number of systems that allow individuals toeasily monitor their blood glucose are currently available. Such systemsinclude electrochemical biosensors, including those that comprise aglucose sensor that is adapted for insertion into a subcutaneous sitewithin the body for the continuous monitoring of glucose levels inbodily fluid of the subcutaneous site (see for example, U.S. Pat. No.6,175,752 to Say et al).

A person may obtain a blood sample by withdrawing blood from a bloodsource in his or her body, such as a vein, using a needle and syringe,for example, or by lancing a portion of his or her skin, using a lancingdevice, for example, to make blood available external to the skin, toobtain the necessary sample volume for in vitro testing. The person maythen apply the fresh blood sample to a test strip, whereupon suitabledetection methods, such as calorimetric, electrochemical, or photometricdetection methods, for example, may be used to determine the person'sactual blood glucose level. The foregoing procedure provides a bloodglucose concentration for a particular or discrete point in time, andthus, must be repeated periodically, in order to monitor blood glucoseover a longer period.

In addition to the discrete or periodic, or in vitro, bloodglucose-monitoring systems described above, at least partiallyimplantable, or in vivo, blood glucose-monitoring systems, which areconstructed to provide continuous in vivo measurement of an individual'sblood glucose concentration, have been described and developed.

Such analyte monitoring devices are constructed to provide forcontinuous or automatic monitoring of analytes, such as glucose, in theblood stream or interstitial fluid. Such devices include electrochemicalsensors, at least a portion of which are operably positioned in a bloodvessel or in the subcutaneous tissue of a user.

While continuous glucose monitoring is desirable, there are severalchallenges associated with optimizing sensor performance for biosensorsconstructed for in vivo use. Accordingly, further development ofmanufacturing techniques and methods, as well as analyte-monitoringdevices, systems, or kits employing the same, is desirable.

SUMMARY

Embodiments of the present disclosure relate to analyte determiningmethods and devices (e.g., electrochemical analyte monitoring systems)that have a membrane with low temperature sensitivity. The sensing layeris disposed on a working electrode of in vivo and/or in vitro analytesensors, e.g., continuous and/or automatic in vivo monitoring usinganalyte sensors and/or test strips. Also provided are systems andmethods of using the, for example electrochemical, analyte sensors inanalyte monitoring.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of various embodiments of the present disclosureis provided herein with reference to the accompanying drawings, whichare briefly described below. The drawings are illustrative and are notnecessarily drawn to scale. The drawings illustrate various embodimentsof the present disclosure and may illustrate one or more embodiment(s)or example(s) of the present disclosure in whole or in part. A referencenumeral, letter, and/or symbol that is used in one drawing to refer to aparticular element may be used in another drawing to refer to a likeelement.

FIG. 1 shows a block diagram of an embodiment of an analyte monitoringsystem according to embodiments of the present disclosure.

FIG. 2 shows a block diagram of an embodiment of a data processing unitof the analyte monitoring system shown in FIG. 1 according toembodiments of the present disclosure.

FIG. 3 shows a block diagram of an embodiment of the primary receiverunit of the analyte monitoring system of FIG. 1 according to embodimentsof the present disclosure.

FIG. 4 shows a schematic diagram of an embodiment of an analyte sensoraccording to the embodiments of the present disclosure.

FIGS. 5A-5B show a perspective view and a cross sectional view,respectively, of an embodiment an analyte sensor according toembodiments of the present disclosure.

FIG. 6 shows a graph of sensor signals (current (nA) over time (hours))for various membrane formulations that include a SMA polymer and apolyetheramine crosslinker over various different temperatures,according to embodiments of the present disclosure.

FIG. 7 shows a graph of sensor signals (current (nA) over time (hours))for various membrane formulations that include a PVPSty polymer and anepoxide-polyether-epoxide crosslinker over various differenttemperatures, according to embodiments of the present disclosure.

FIG. 8 shows a graph of sensor signals (current (nA) over time (hours))for various membrane formulations that include a PVPSty polymer, a Pegcrosslinker and a Ppg crosslinker over various different temperatures,according to embodiments of the present disclosure.

FIG. 9 shows a graph of sensor signals (current (nA) over time (hours))for various membrane formulations that include a PEO-PVP polymer and aPpg crosslinker over various different temperatures, according toembodiments of the present disclosure.

FIG. 10 shows a graph of sensor signals (current (nA) over time (hours))for a membrane formulations that includes a PEO-PVP polymer, a PVP-Sty(30%) polymer, and a Ppg crosslinker over various differenttemperatures, according to embodiments of the present disclosure.

DETAILED DESCRIPTION

Before the embodiments of the present disclosure are described, it is tobe understood that this invention is not limited to particularembodiments described, as such may, of course, vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting, since the scope of the embodiments of the invention will bedefined by the appended claims.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassedwithin the invention. The upper and lower limits of these smaller rangesmay independently be included or excluded in the range, and each rangewhere either, neither or both limits are included in the smaller rangesis also encompassed within the invention, subject to any specificallyexcluded limit in the stated range. Where the stated range includes oneor both of the limits, ranges excluding either or both of those includedlimits are also included in the invention.

In the description of the invention herein, it will be understood that aword appearing in the singular encompasses its plural counterpart, and aword appearing in the plural encompasses its singular counterpart,unless implicitly or explicitly understood or stated otherwise. Merelyby way of example, reference to “an” or “the” “analyte” encompasses asingle analyte, as well as a combination and/or mixture of two or moredifferent analytes, reference to “a” or “the” “concentration value”encompasses a single concentration value, as well as two or moreconcentration values, and the like, unless implicitly or explicitlyunderstood or stated otherwise. Further, it will be understood that forany given component described herein, any of the possible candidates oralternatives listed for that component, may generally be usedindividually or in combination with one another, unless implicitly orexplicitly understood or stated otherwise. Additionally, it will beunderstood that any list of such candidates or alternatives, is merelyillustrative, not limiting, unless implicitly or explicitly understoodor stated otherwise.

Various terms are described below to facilitate an understanding of theinvention. It will be understood that a corresponding description ofthese various terms applies to corresponding linguistic or grammaticalvariations or forms of these various terms. It will also be understoodthat the invention is not limited to the terminology used herein, or thedescriptions thereof, for the description of particular embodiments.Merely by way of example, the invention is not limited to particularanalytes, bodily or tissue fluids, blood or capillary blood, or sensorconstructs or usages, unless implicitly or explicitly understood orstated otherwise, as such may vary.

The publications discussed herein are provided solely for theirdisclosure prior to the filing date of the application. Nothing hereinis to be construed as an admission that the embodiments of the inventionare not entitled to antedate such publication by virtue of priorinvention. Further, the dates of publication provided may be differentfrom the actual publication dates which may need to be independentlyconfirmed.

Systems and Methods Using Membranes with Low Temperature Sensitivity

Embodiments of the present disclosure relate to methods and devices forreducing the temperature sensitivity of a membrane of a sensor byinclusion of one or more polymers and one or more crosslinkers. Themembrane may be a sensing layer or a membrane configured to limit theflux of an analyte to the sensing layer, where the sensing layer isdisposed on a working electrode of the sensor, such as in vivo and/or invitro analyte sensors, including, for example, continuous and/orautomatic in vivo analyte sensors. Embodiments of the present disclosureprovide for inclusion of one or more polymers and one or morecrosslinkers in a solution, such as a membrane formulation, resulting ina reduction in temperature sensitivity of the membrane, thereby reducingfluctuations in the signal from the sensor due to changes intemperature. Also provided are systems and methods of using the analytesensors in analyte monitoring.

The term “polymer” refers to a large molecule (e.g., a macromolecule)that includes repeating structural units (e.g., monomers). Thesesubunits are typically connected by covalent chemical bonds. Polymersmay be branched or unbranched. Polymers may be homopolymers, which arepolymers formed by polymerization of a single type of monomer. In otherembodiments, polymers are heteropolymers (e.g., copolymers) that includetwo or more different types of monomers. Copolymers can have alternatingmonomer subunits, or in some cases, may be block copolymers, whichinclude two or more homopolymer subunits linked by covalent bonds. Forexample, block copolymers with two blocks of two distinct chemicalspecies (e.g., A and B) are called diblock copolymers, and blockcopolymers with three blocks of two distinct chemical species (e.g., Aand B) are called triblock copolymers.

In certain embodiments, polymers are crosslinked by a crosslinker (e.g.,a crosslinking agent). A “crosslinker” is a molecule that contains atleast two reactive groups capable of linking at least two molecules(e.g., polymers) together, or linking at least two portions of the samemolecule together. Linking of at least two molecules is calledintermolecular crosslinking, while linking of at least two portions ofthe same molecule is called intramolecular crosslinking. A crosslinkerhaving more than two reactive groups may be capable of bothintermolecular and intramolecular crosslinkings at the same time.

Embodiments of the present disclosure are based on the discovery thatthe addition of one or more polymers and one or more crosslinkers tosolution formulations used in the manufacture of in vivo and/or in vitrobiosensors reduces the temperature sensitivity of a membrane layer ofthe sensor (e.g., a membrane configured to limit the flux of an analyteto the sensing layer of the sensor). Biocompatible membranes ofembodiments of the present disclosure can include one or more polymersand one or more crosslinkers. In some cases, the one or more polymersand one or more crosslinkers form a membrane that includes a crosslinkedpolymer.

During the manufacturing process for the subject analyte sensors, anaqueous solution (e.g., a sensing layer) is contacted with a surface ofa substrate (e.g., a surface of a working electrode), forming adeposition of the sensing layer solution on the surface of thesubstrate. In some cases, a membrane solution is contacted with asurface of the sensing layer, forming a deposition of the membranesolution on the surface of the sensing layer.

In some instances, the membrane may form one or more bonds with thesensing layer. By bonds is meant any type of an interaction betweenatoms or molecules that allows chemical compounds to form associationswith each other, such as, but not limited to, covalent bonds, ionicbonds, dipole-dipole interactions, hydrogen bonds, London dispersionforces, and the like. For example, in situ polymerization of themembrane can form crosslinks between the polymers of the membrane andthe polymers in the sensing layer. In certain embodiments, crosslinkingof the membrane to the sensing layer facilitates a reduction in theoccurrence of delamination of the membrane from the sensing layer.

In certain embodiments of the present disclosure, the membrane solutionincludes one or more polymers and one or more crosslinkers. In certaininstances, the one or more polymers and one or more crosslinkers reducesthe temperature sensitivity of the membrane. By “temperaturesensitivity” is meant changes in the signal from a sensor due to changesin temperature. For example, the sensor signal may increase withincreasing temperature, and correspondingly, the sensor signal maydecrease with decreasing temperature. Examples of typical analyte sensormembranes are found in U.S. Pat. No. 6,932,894 and U.S. ApplicationPublication No. 2008/0179187, published on Jul. 31, 2008, thedisclosures of each of which are hereby incorporated by reference intheir entirety.

Generally, for analyte flux limiting membranes, the flux of an analytethrough the membrane, and thus the resulting signal from the sensor, maydepend on the temperature sensitivity of the membrane. For example, theflux of an analyte through the membrane may increase as the temperatureincreases and decrease as the temperature decreases. In these examples,when the temperature increases, the diffusivity of solutes (e.g.,glucose) through the membrane increases, and when the temperaturedecreases, the diffusivity of solutes (e.g., glucose) through themembrane decreases. Typical analyte flux limiting membranes may have atemperature sensitivity of 10%/° C. or more over a range oftemperatures. As such, typical analyte sensors may need to correct forfluctuations in sensor signal due to changes in temperature. Forexample, typical analyte sensors may include additional hardware, suchas temperature sensors, to measure the skin temperature of the subject.However, temperature measurements may include errors due to differencesbetween the skin surface temperature and the actual subcutaneoustemperature at the point of analyte measurement.

In certain embodiments of the present disclosure, without being limitedto any particular theory, membranes with low temperature sensitivity mayhave substantially the same diffusivity to solutes (e.g., glucose) overa temperature range of interest. In some instances, the dependence ofthe sensor signal on temperature may depend on the lower criticalsolution temperature (LCST) of the membrane. The LCST is the criticaltemperature below which the components of a mixture are miscible. TheLCST may depend on pressure (e.g., increasing pressure may increase theLCST), degree of polymerization, polydispersity (e.g., the distributionof molecular mass in the polymer), branching of the polymer, and thelike. Above the LCST, one or more polymers may be immiscible (e.g., oneor more polymers may solidify or crystalize), which may result in adecrease in the diffusivity of the membrane. In certain instances, thisdecrease in the diffusivity of the membrane may substantially offset theincrease in diffusivity due to increasing the temperature, such that themembrane has substantially the same diffusivity to solutes (e.g.,glucose) over a temperature range of interest. In some instances, thetemperature range of interest includes normal body temperature for ahuman, such as a temperature range from 25° C. to 60° C., or from 25° C.to 55° C., or from 30° C. to 50° C., or from 35° C. to 45° C.

In certain embodiments, the analyte sensor is configured such that asignal from the analyte sensor changes 10%/° C. or less over a range oftemperatures, or 7.5%/° C. or less over a range of temperatures, forinstance 5%/° C. or less over a range of temperatures, or 4%/° C. orless over a range of temperatures, or 3%/° C. or less over a range oftemperatures, or 2%/° C. or less over a range of temperatures, or 1%/°C. or less over a range of temperatures, or 0.5%/° C. or less over arange of temperatures, or 0.1%/° C. or less over a range oftemperatures. In certain instances, sensors that include a membraneformulation as disclosed herein have a sensitivity of 0.1 nA/mM or more,or 0.5 nA/mM or more, such as 1 nA/mM or more, including 1.5 nA/mM ormore, for instance 2 nA/mM or more, or 2.5 nA/mM or more, or 5 nA/mM ormore, or 7.5 nA/mM or more, or 10 nA/mM or more, or 12.5 nA/mM or more,or 15 nA/mM or more.

In some cases, a sensor that has a membrane that includes one or morepolymers and one or more crosslinkers as disclosed herein has an initialsensitivity. The sensor may have a sensitivity that is 90% or more ofthe initial sensitivity after 1 day or more, such as 2 days or more, 3days or more, 4 days or more, 5 days or more, 6 days or more, 7 days ormore, 10 days or more, 14 days or more, 1 month or more, 2 months ormore, 4 months or more, 6 months or more, 9 months or more, or 1 year ormore. For example, the sensor may maintain 95% or more of its initialsensitivity after 1 day or more, such as 2 days or more, 3 days or more,4 days or more, 5 days or more, 6 days or more, 7 days or more, 10 daysor more, 14 days or more, 1 month or more, 2 months or more, 4 months ormore, 6 months or more, 9 months or more, or 1 year or more. In somecases, the sensor maintains 97% or more of its initial sensitivity after1 day or more, such as 2 days or more, 3 days or more, 4 days or more, 5days or more, 6 days or more, 7 days or more, 10 days or more, 14 daysor more, 1 month or more, 2 months or more, 4 months or more, 6 monthsor more, 9 months or more, or 1 year or more. In certain instances, thesensor may maintain 99% or more of its initial sensitivity after 1 dayor more, such as 2 days or more, 3 days or more, 4 days or more, 5 daysor more, 6 days or more, 7 days or more, 10 days or more, 14 days ormore, 1 month or more, 2 months or more, 4 months or more, 6 months ormore, 9 months or more, or 1 year or more.

Membranes Incorporating a Poly(Styrene-Co-Maleic Anhydride) Polymer anda Polyetheramine Crosslinker

In certain embodiments, the analyte sensor includes a membrane disposedon the sensing layer, where the membrane includes apoly(styrene-co-maleic anhydride) polymer and a polyetheraminecrosslinker.

In some instances, the poly(styrene-co-maleic anhydride) polymer (SMApolymer) has a styrene composition ranging from 10% to 90%, includingfrom 25% to 90%, such as from 50% to 90%. For example, the SMA polymermay have a styrene composition of 75%. In some embodiments, the SMApolymer has a molecular weight of 1000 or more, such as 1500 or more,including 2000 or more. For instance, the SMA polymer may have amolecular weight of 1900.

In certain embodiments, the SMA polymer includes a compound of theformula:

where m and n are each positive integers. The * denotes a bond toanother group, for example a SMA polymer of the formula above.

In some cases, the polyetheramine crosslinker is a poly(propyleneglycol)-block-poly(ethylene glycol)-block-poly(propylene glycol)bis(2-aminopropyl ether) crosslinker, such as but not limited to aJeffamine® ED-900 crosslinker, available from Huntsman InternationalLLC, Salt Lake City, Utah. In some embodiments, the polyetheraminecrosslinker has a molecular weight of 500 or more, such as 700 or more,including 1000 or more. For instance, the polyetheramine crosslinker mayhave a molecular weight of 900. In some embodiments, the polyetheraminecrosslinker is a poly(ethylene glycol)-block-poly(propyleneglycol)-block-poly(ethylene glycol) 2-aminopropyl ether crosslinker.

In certain embodiments, the crosslinker includes a compound of theformula:

where x, y and z are each integers, with the proviso that either x or zis optionally 0, and where OR′ and OR″ are each either normal or isopropylene oxide. For instance, if x is 0, then z is a positive integer,or if z is 0, then x is a positive integer, such that either x or z maybe 0, but x and z are not both 0.

In certain instances, the polyetheramine crosslinker has a ratio ofy:(x+z) that is 10:5 or more, such as 12.5:6 or more, including 15:7 ormore, for instance 9:3.5 or more. For example, the polyetheraminecrosslinker may have a ratio of y:(x+z) that is 12.5:6.

In some instances, a membrane that includes a SMA polymer and apolyetheramine crosslinker has the following formula:

where m and n are each positive integers, and where x, y and z are eachintegers, with the proviso that either x or z is optionally 0, and whereOR′ and OR″ are each either normal or iso propylene oxide. For instance,as described above, if x is 0, then z is a positive integer, or if z is0, then x is a positive integer, such that either x or z may be 0, but xand z are not both 0. The * denotes a bond to another group, for examplea SMA polymer of the formula above. In some cases, as described above,the ratio of y:(x+z) is 10:5 or more, such as 12.5:6 or more, including15:7 or more, for instance 9:3.5 or more. For example, thepolyetheramine crosslinker may have a ratio of y:(x+z) that is 12.5:6.

In certain embodiments, analyte sensors that have a membrane thatincludes a SMA polymer and a polyetheramine crosslinker are configuredsuch that a signal from the analyte sensor changes 5%/° C. or less overa range of temperatures, or 2%/° C. or less over a range oftemperatures, or 1.5%/° C. or less over a range of temperatures, or 1%/°C. or less over a range of temperatures, or 0.7%/° C. or less over arange of temperatures, or 0.5%/° C. or less over a range oftemperatures, or 0.4%/° C. or less over a range of temperatures, or0.3%/° C. or less over a range of temperatures, or 0.2%/° C. or lessover a range of temperatures, or 0.1%/° C. or less over a range oftemperatures. In certain instances, analyte sensors that have a membranethat includes a SMA polymer and a polyetheramine crosslinker asdisclosed herein have a sensitivity of 0.5 nA/mM or more, or 0.7 nA/mMor more, such as 1 nA/mM or more, including 1.5 nA/mM or more, forinstance 2 nA/mM or more, or 2.5 nA/mM or more, or 3 nA/mM or more, or3.5 nA/mM or more, or 4 nA/mM or more.

Membranes Incorporating a Poly(4-Vinylpyridine)-Co-Polystyrene Polymerand an Epoxide-Polyether-Epoxide Crosslinker

In certain embodiments, the analyte sensor includes a membrane disposedon the sensing layer, where the membrane includes apoly(4-vinylpyridine)-co-polystyrene polymer and anepoxide-polyether-epoxide crosslinker.

In certain embodiments, the poly(4-vinylpyridine)-co-polystyrene polymer(PVPSty polymer) includes a compound of the formula:

where x and y are each positive integers. The * denotes a bond toanother group, for example a PVPSty polymer of the formula above.

In some cases, the epoxide-polyether-epoxide crosslinker (e.g.,epoxide-polyethylene oxide-polypropylene oxide-polyethyleneoxide-epoxide (i.e., epoxide-PEO-PPO-PEO-epoxide) crosslinker orepoxide-polypropylene oxide-polyethylene oxide-polypropyleneoxide-epoxide (i.e., epoxide-PPO-PEO-PPO-epoxide) crosslinker) includesa compound of the formula:

where m, n and o are each integers, with the proviso that either m or ois optionally 0, and where R′ and R″ are each a linking group, such as asubstituted or unsubstituted alkyl, a substituted or unsubstitutedheteroalkyl, or a substituted or unsustituted amine. For instance, if mis 0, then o is a positive integer, or if o is 0, then m is a positiveinteger, such that either m or o may be 0, but m and o are not both 0.EO denotes an ethylene oxide group and PO denotes a propylene oxidegroup, where the propylene oxide group may be normal or iso propyleneoxide.

For example, the epoxide-polyether-epoxide crosslinker may be anepoxide-PEO-PPO-PEO-epoxide crosslinker, such as a compound of thefollowing formula:

where m, n and o are each integers, with the proviso that either m or ois optionally 0, as described above.

The epoxide-PEO-PPO-PEO-epoxide crosslinker may be formed by thefollowing reaction:

In certain embodiments, the epoxide-polyether-epoxide crosslinker is anepoxide-PPO-PEO-PPO-epoxide crosslinker, such as a compound of thefollowing formula:

where m, n and o are each integers, with the proviso that either m or ois optionally 0, as described above.

The epoxide-PPO-PEO-PPO-epoxide crosslinker may be formed by thefollowing reaction:

In some instances, a membrane that includes a PVPSty polymer and anepoxide-polyether-epoxide crosslinker has the following formula:

where x and y are each positive integers, and where m, n and o are eachintegers, with the proviso that either m or o is optionally 0, and whereR′ and R″ are each a linking group, such as a substituted orunsubstituted alkyl, a substituted or unsubstituted heteroalkyl, or asubstituted or unsubstituted amine. For instance, if m is 0, then o is apositive integer, or if o is 0, then m is a positive integer, such thateither m or o may be 0, but m and o are not both 0. EO denotes anethylene oxide group and PO denotes a propylene oxide group, where thepropylene oxide group may be normal or iso propylene oxide. The *denotes a bond to another group, for example a PVPSty polymer asdescribed above.

For example, a membrane that includes a PVPSty polymer and anepoxide-polyether-epoxide crosslinker may have the following formula:

where x and y are each positive integers, and m, n and o are eachintegers, with the proviso that either m or o is optionally 0. The *denotes a bond to another group, for example a PVPSty polymer asdescribed above.

In certain embodiments, analyte sensors that have a membrane thatincludes a PVPSty polymer and an epoxide-polyether-epoxide crosslinkerare configured such that a signal from the analyte sensor changes 5%/°C. or less over a range of temperatures, or 4%/° C. or less over a rangeof temperatures, for instance 3.5%/° C. or less over a range oftemperatures, or 3%/° C. or less over a range of temperatures, or 2.5%/°C. or less over a range of temperatures, or 2%/° C. or less over a rangeof temperatures, or 1.5%/° C. or less over a range of temperatures, or1%/° C. or less over a range of temperatures, or 0.5%/° C. or less overa range of temperatures. In certain instances, analyte sensors that havea membrane that includes a PVPSty polymer and anepoxide-polyether-epoxide crosslinker as disclosed herein have asensitivity of 1 nA/mM or more, or 2 nA/mM or more, such as 3 nA/mM ormore, including 4 nA/mM or more, for instance 5 nA/mM or more, or 7.5nA/mM or more, or 10 nA/mM or more, or 12.5 nA/mM or more, or 15 nA/mMor more.

Membranes Incorporating a Poly(4-Vinylpyridine)-Co-Polystyrene Polymer,a Poly(Ethylene Glycol) (n) Diglycidyl Ether Crosslinker, and aPoly(Propylene Glycol) (n) Diglycidyl Ether Crosslinker

In certain embodiments, the analyte sensor includes a membrane disposedon the sensing layer, where the membrane includes apoly(4-vinylpyridine)-co-polystyrene polymer, a poly(ethylene glycol)(n) diglycidyl ether crosslinker, and a poly(propylene glycol) (n)diglycidyl ether crosslinker.

In certain embodiments, the poly(4-vinylpyridine)-co-polystyrene polymer(PVPSty polymer) includes a compound of the formula:

where x and y are each positive integers.

In some cases, the a poly(ethylene glycol) (n) diglycidyl ethercrosslinker (Peg crosslinker) includes a compound of the formula:

where m is a positive integer.

In certain instances, the poly(propylene glycol) (n) diglycidyl ethercrosslinker (Ppg crosslinker) includes a compound of the formula:

where OR is either normal or iso propylene oxide, and n is a positiveinteger.

In certain embodiments, a membrane that includes a PVPSty polymer, a Pegcrosslinker and a Ppg crosslinker has the following formula:

where x and y are each positive integers, m and n are each positiveintegers, and r and q are each positive integers. EO denotes an ethyleneoxide group and PO denotes a propylene oxide group, where the propyleneoxide group may be normal or iso propylene oxide. The * denotes a bondto another group, for example a PVPSty polymer as described above.

In certain embodiments, analyte sensors that include a PVPSty polymer, aPeg crosslinker and a Ppg crosslinker are configured such that a signalfrom the analyte sensor changes 5%/° C. or less over a range oftemperatures, or 4.5%/° C. or less over a range of temperatures, forinstance 4%/° C. or less over a range of temperatures, or 3.5%/° C. orless over a range of temperatures, or 3%/° C. or less over a range oftemperatures, or 2.5%/° C. or less over a range of temperatures, or 2%/°C. or less over a range of temperatures, or 1.5%/° C. or less over arange of temperatures, or 1%/° C. or less over a range of temperatures.In certain instances, analyte sensors that have a membrane that includesa PVPSty polymer, a Peg crosslinker and a Ppg crosslinker as disclosedherein have a sensitivity of 1 nA/mM or more, or 2.5 nA/mM or more, suchas 5 nA/mM or more, including 7.5 nA/mM or more, for instance 10 nA/mMor more, or 12.5 nA/mM or more, or 15 nA/mM or more.

Membranes Incorporating a Poly(Ethylene Oxide-b-4-Vinyl Pyridine)Polymer and a Poly(Propylene Glycol) (n) Diglycidyl Ether Crosslinker

In certain embodiments, the analyte sensor includes a membrane disposedon the sensing layer, where the membrane includes a poly(ethyleneoxide-b-4-vinyl pyridine) polymer and a poly(propylene glycol) (n)diglycidyl ether crosslinker.

In some instances, the poly(ethylene oxide-b-4-vinyl pyridine) polymer(PEO-PVP polymer) has a composition characterized by a molecular weightof the PEO portion to the PVP portion of 2000(PEO)-b-10000(PVP). Incertain cases, the PEO-PVP polymer has a polydispersity index (PDI) of 1or more, such as 1.5 or more, or 2 or more, or 5 or more. For examplethe PEO-PVP polymer may have a PDI of 1.25. PDI calculated as the weightaverage molecular weight divided by the number average molecular weightand indicates the distribution of individual molecular masses in a batchof polymers.

In certain embodiments, the PEO-PVP polymer includes a compound of theformula:

where m and n are each positive integers. The * denotes a bond toanother group, for example a PEO-PVP polymer as described above.

In some cases, the poly(propylene glycol) (n) diglycidyl ethercrosslinker (Ppg crosslinker) includes a compound of the formula:

where OR is either normal or iso propylene oxide, and where x is apositive integer.

In some instances, a membrane that includes a PEO-PVP polymer and a Ppgcrosslinker has the following formula:

where m and n are each positive integers, x is a positive integer, andOR is either normal or iso propylene oxide. The * denotes a bond toanother group, for example a PEO-PVP polymer as described above.

In certain embodiments, analyte sensors that have a membrane thatincludes a PEO-PVP polymer and a Ppg crosslinker are configured suchthat a signal from the analyte sensor changes 10%/° C. or less over arange of temperatures, or 7.5%/° C. or less over a range oftemperatures, for instance 5%/° C. or less over a range of temperatures,or 4.5%/° C. or less over a range of temperatures, or 4%/° C. or lessover a range of temperatures, or 3.5%/° C. or less over a range oftemperatures, or 3%/° C. or less over a range of temperatures, or 2.5%/°C. or less over a range of temperatures, or 2%/° C. or less over a rangeof temperatures, or 1.5%/° C. or less over a range of temperatures, or1%/° C. or less over a range of temperatures. In certain instances,analyte sensors that have a membrane that includes a PEO-PVP polymer anda Ppg crosslinker as disclosed herein have a sensitivity of 0.1 nA/mM ormore, or 0.5 nA/mM or more, such as 1 nA/mM or more, including 1.5 nA/mMor more, for instance 2 nA/mM or more, or 2.5 nA/mM or more, or 3 nA/mMor more, or 3.5 nA/mM or more, or 4 nA/mM or more, or 4.5 nA/mM or more,or 5 nA/mM or more.

Membranes Incorporating a Poly(Ethylene Oxide-b-4-Vinyl Pyridine)Polymer, a Poly(4-Vinylpyridine)-Co-Polystyrene Polymer, and aPoly(Propylene Glycol) (n) Diglycidyl Ether Crosslinker

In certain embodiments, the analyte sensor includes a membrane disposedon the sensing layer, where the membrane includes a poly(ethyleneoxide-b-4-vinyl pyridine) polymer, apoly(4-vinylpyridine)-co-polystyrene polymer, and a poly(propyleneglycol) (n) diglycidyl ether crosslinker.

In some instances, the poly(ethylene oxide-b-4-vinyl pyridine) polymer(PEO-PVP polymer) has a composition characterized by a molecular weightof the PEO portion to the PVP portion of 2000(PEO)-b-10000(PVP). Incertain cases, the PEO-PVP polymer has a polydispersity index (PDI) of 1or more, such as 1.5 or more, or 2 or more, or 5 or more. For examplethe PEO-PVP polymer may have a PDI of 1.25.

In certain embodiments, the PEO-PVP polymer includes a compound of theformula:

where m and n are each positive integers. The * denotes a bond toanother group, for example a PEO-PVP polymer as described above.

In some instances, the poly(4-vinylpyridine)-co-polystyrene polymer(PVPSty polymer) has a styrene composition ranging from 10% to 90%,including from 10% to 75%, such as from 10% to 50%. For example, thePVPSty polymer may have a styrene composition of 30%. In certainembodiments, the PVPSty polymer includes a compound of the formula:

where x and y are each positive integers. The ** denotes a bond toanother group, for example a PVPSty polymer as described above.

In some cases, the poly(propylene glycol) (n) diglycidyl ethercrosslinker (Ppg crosslinker) includes a compound of the formula:

where OR is either normal or iso propylene oxide, and where z is apositive integer.

In some instances, a membrane that includes a PEO-PVP polymer, a PVPStypolymer and a Ppg crosslinker has the following formula:

where m and n are each positive integers, x and y are each positiveintegers, z is a positive integer, and OR is either normal or isopropylene oxide. The * denotes a bond to another group, for example aPEO-PVP polymer as described above. The ** denotes a bond to anothergroup, for example a PVPSty polymer as described above.

In certain embodiments, analyte sensors that have a membrane thatincludes a PEO-PVP polymer, a PVPSty polymer and a Ppg crosslinker areconfigured such that a signal from the analyte sensor changes 10%/° C.or less over a range of temperatures, or 7.5%/° C. or less over a rangeof temperatures, for instance 5%/° C. or less over a range oftemperatures, or 4.5%/° C. or less over a range of temperatures, or 4%/°C. or less over a range of temperatures, or 3.5%/° C. or less over arange of temperatures, or 3%/° C. or less over a range of temperatures,or 2.5%/° C. or less over a range of temperatures, or 2%/° C. or lessover a range of temperatures, or 1.5%/° C. or less over a range oftemperatures, or 1%/° C. or less over a range of temperatures. Incertain instances, analyte sensors that have a membrane that includes aPEO-PVP polymer, a PVPSty polymer and a Ppg crosslinker as disclosedherein have a sensitivity of 0.1 nA/mM or more, or 0.5 nA/mM or more,such as 1 nA/mM or more, including 1.5 nA/mM or more, for instance 2nA/mM or more, or 2.5 nA/mM or more, or 3 nA/mM or more, or 3.5 nA/mM ormore, or 4 nA/mM or more, or 4.5 nA/mM or more, or 5 nA/mM or more.

Additional embodiments of a sensor that may be suitably formulated withthe polymers and crosslinkers disclosed herein are described in U.S.Pat. Nos. 5,262,035, 5,262,305, 6,134,461, 6,143,164, 6,175,752,6,338,790, 6,579,690, 6,605,200, 6,605,201, 6,654,625, 6,736,957,6,746,582, 6,932,894, 7,090,756 as well as those described in U.S.patent application Ser. Nos. 11/701,138, 11/948,915, 12/625,185,12/625,208, and 12/624,767, the disclosures of all of which areincorporated herein by reference in their entirety. Moreover,embodiments of the present disclosure may be incorporated intobattery-powered or self-powered analyte sensors, in one embodiment theanalyte sensor is a self-powered sensor, such as disclosed in U.S.patent application Ser. No. 12/393,921 (U.S. Application Publication No.2010/0213057).

Methods of Making Analyte Sensor Membranes

An example of a process for producing a membrane is now described. Forexample, the polymer and a suitable crosslinker may be dissolved in abuffer-containing solvent to produce a membrane solution. In certaininstances, the solvent is a buffer-alcohol mixed solvent. In someembodiments, the buffer has a pH of about 7.5 to about 9.5 and thealcohol is ethanol. For example, the buffer may include a 10 mM(2-(4-(2-hydroxyethyl)-1-piperazine)ethanesulfonate) (HEPES) buffer (pH8) and the ethanol to buffer volume ratio may range from 95 to 5 to 0 to100. In certain instances, a minimum amount of buffer is used for thecrosslinking chemistry. The amount of solvent needed to dissolve thepolymer and the crosslinker may vary depending on the nature of thepolymer and the crosslinker. For example, a higher percentage of alcoholmay be required to dissolve a relatively hydrophobic polymer and/orcrosslinker.

In certain embodiments, the composition of the final membrane may dependon the ratio of polymer to cross-linker. By way of example, if a smallamount of crosslinker or a large excess of polymer is used, crosslinkingmay be insufficient and the resulting membrane may be weak. Further, ifa more than adequate amount of crosslinker is used, the resultingmembrane may be overly crosslinked, such that the membrane is toobrittle and/or impedes analyte diffusion. Thus, membranes may beformulated with a particular ratio of a given polymer to a givencrosslinker. By way of example, the polymer to crosslinker ratio byweight may range from 2:1 to 50:1, such as from 2:1 to 40:1, includingfrom 2:1 to 30:1, or from 2:1 to 25:1, or from 3:1 to 22:1, or from 4:1to 20:1 or from 5:1 to 15:1, and the like.

In certain embodiments, it is desirable to have a slow crosslinkingreaction during the dispensing of membrane solution so that the membranesolution has a reasonable pot-life for large-scale manufacture. A fastcrosslinking reaction results in a membrane solution of rapidly changingviscosity, which in some cases may make application of the membranesolution to the analyte sensor difficult. For example, the crosslinkingreaction may be slow during the dispensing of the membrane solution, andaccelerated during the curing of the membrane at ambient temperature, orat an elevated temperature.

The membrane solution can be coated over a variety of biosensors thatmay benefit from having a membrane disposed over the sensing layer.Examples of such biosensors include, but are not limited to, glucosesensors and lactate sensors, which are described, for example in U.S.Pat. No. 6,134,461 to Heller et al., the disclosure of which isincorporated herein in its entirety by reference. The coating processmay include any desirable technique, such as spin-coating, dip-coating,doctor blading or dispensing droplets of the membrane solution over thesensing layers, and the like. In some cases, after application of themembrane solution to the analyte sensor, the membrane is cured underambient conditions, such as 1 to 2 days. The particular details of thecoating process (such as dip duration, dip frequency, number of dips,and the like) may vary depending on the polymer and/or crosslinker usedand the resulting membrane desired. In certain embodiments, sensorfabrication may include depositing an enzyme-containing sensing layerover a working electrode and casting a diffusion-limiting membrane layerover the sensing layer, and optionally, also over the counter andreference electrodes. Sensors having other configurations such as athree-electrode design can also be prepared using similar methods.

Electrochemical Sensors

Embodiments of the present disclosure relate to methods and devices fordetecting at least one analyte, including glucose, in body fluid.Embodiments relate to the continuous and/or automatic in vivo monitoringof the level of one or more analytes using a continuous analytemonitoring system that includes an analyte sensor at least a portion ofwhich is to be positioned beneath a skin surface of a user for a periodof time and/or the discrete monitoring of one or more analytes using anin vitro blood glucose (“BG”) meter and an analyte test strip.Embodiments include combined or combinable devices, systems and methodsand/or transferring data between an in vivo continuous system and an invivo system. In some embodiments, the systems, or at least a portion ofthe systems, are integrated into a single unit.

A sensor as described herein may be an in vivo sensor or an in vitrosensor (i.e., a discrete monitoring test strip). Such a sensor can beformed on a substrate, e.g., a substantially planar substrate. Incertain embodiments, the sensor is a wire, e.g., a working electrodewire inner portion with one or more other electrodes associated (e.g.,on, including wrapped around) therewith. The sensor may also include atleast one counter electrode (or counter/reference electrode) and/or atleast one reference electrode or at least one reference/counterelectrode.

Accordingly, embodiments include analyte monitoring devices and systemsthat include an analyte sensor at least a portion of which ispositionable beneath the skin surface of the user for the in vivodetection of an analyte, including glucose, lactate, and the like, in abody fluid. Embodiments include wholly implantable analyte sensors andanalyte sensors in which only a portion of the sensor is positionedunder the skin and a portion of the sensor resides above the skin, e.g.,for contact to a sensor control unit (which may include a transmitter),a receiver/display unit, transceiver, processor, etc. The sensor may be,for example, subcutaneously positionable in a user for the continuous orperiodic monitoring of a level of an analyte in the user's interstitialfluid. For the purposes of this description, continuous monitoring andperiodic monitoring will be used interchangeably, unless notedotherwise. The sensor response may be correlated and/or converted toanalyte levels in blood or other fluids. In certain embodiments, ananalyte sensor may be positioned in contact with interstitial fluid todetect the level of glucose, which detected glucose may be used to inferthe glucose level in the user's bloodstream. Analyte sensors may beinsertable into a vein, artery, or other portion of the body containingfluid. Embodiments of the analyte sensors may be configured formonitoring the level of the analyte over a time period which may rangefrom seconds, minutes, hours, days, weeks, to months, or longer.

In certain embodiments, the analyte sensors, such as glucose sensors,are capable of in vivo detection of an analyte for one hour or more,e.g., a few hours or more, e.g., a few days or more, e.g., three or moredays, e.g., five days or more, e.g., seven days or more, e.g., severalweeks or more, or one month or more. Future analyte levels may bepredicted based on information obtained, e.g., the current analyte levelat time t₀, the rate of change of the analyte, etc. Predictive alarmsmay notify the user of a predicted analyte levels that may be of concernin advance of the user's analyte level reaching the future predictedanalyte level. This provides the user an opportunity to take correctiveaction.

In an electrochemical embodiment, the sensor is placed,transcutaneously, for example, into a subcutaneous site such thatsubcutaneous fluid of the site comes into contact with the sensor. Inother in vivo embodiments, placement of at least a portion of the sensormay be in a blood vessel. The sensor operates to electrolyze an analyteof interest in the subcutaneous fluid or blood such that a current isgenerated between the working electrode and the counter electrode. Avalue for the current associated with the working electrode isdetermined. If multiple working electrodes are used, current values fromeach of the working electrodes may be determined. A microprocessor maybe used to collect these periodically determined current values or tofurther process these values.

If an analyte concentration is successfully determined, it may bedisplayed, stored, transmitted, and/or otherwise processed to provideuseful information. By way of example, raw signal or analyteconcentrations may be used as a basis for determining a rate of changein analyte concentration, which should not change at a rate greater thana predetermined threshold amount. If the rate of change of analyteconcentration exceeds the predefined threshold, an indication maybedisplayed or otherwise transmitted to indicate this fact. In certainembodiments, an alarm is activated to alert a user if the rate of changeof analyte concentration exceeds the predefined threshold.

As demonstrated herein, the methods of the present disclosure are usefulin connection with a device that is used to measure or monitor ananalyte (e.g., glucose), such as any such device described herein. Thesemethods may also be used in connection with a device that is used tomeasure or monitor another analyte (e.g., ketones, ketone bodies, HbA1c,and the like), including oxygen, carbon dioxide, proteins, drugs, oranother moiety of interest, for example, or any combination thereof,found in bodily fluid, including subcutaneous fluid, dermal fluid(sweat, tears, and the like), interstitial fluid, or other bodily fluidof interest, for example, or any combination thereof. In general, thedevice is in good contact, such as thorough and substantially continuouscontact, with the bodily fluid.

According to embodiments of the present disclosure, the measurementsensor is one suited for electrochemical measurement of analyteconcentration, for example glucose concentration, in a bodily fluid. Inthese embodiments, the measurement sensor includes at least a workingelectrode and a counter electrode. Other embodiments may further includea reference electrode. The working electrode is typically associatedwith a glucose-responsive enzyme. A mediator may also be included. Incertain embodiments, hydrogen peroxide, which may be characterized as amediator, is produced by a reaction of the sensor and may be used toinfer the concentration of glucose. In some embodiments, a mediator isadded to the sensor by a manufacturer, i.e., is included with the sensorprior to use. The redox mediator may be disposed relative to the workingelectrode and is capable of transferring electrons between a compoundand a working electrode, either directly or indirectly. The redoxmediator may be, for example, immobilized on the working electrode,e.g., entrapped on a surface or chemically bound to a surface.

FIG. 1 shows a data monitoring and management system such as, forexample, an analyte (e.g., glucose) monitoring system 100 in accordancewith certain embodiments. Aspects of the subject disclosure are furtherdescribed primarily with respect to glucose monitoring devices andsystems, and methods of glucose detection, for convenience only and suchdescription is in no way intended to limit the scope of the embodiments.It is to be understood that the analyte monitoring system may beconfigured to monitor a variety of analytes at the same time or atdifferent times.

Analytes that may be monitored include, but are not limited to, acetylcholine, amylase, bilirubin, cholesterol, chorionic gonadotropin,glycosylated hemoglobin (HbA 1c), creatine kinase (e.g., CK-MB),creatine, creatinine, DNA, fructosamine, glucose, glucose derivatives,glutamine, growth hormones, hormones, ketones, ketone bodies, lactate,peroxide, prostate-specific antigen, prothrombin, RNA, thyroidstimulating hormone, and troponin. The concentration of drugs, such as,for example, antibiotics (e.g., gentamicin, vancomycin, and the like),digitoxin, digoxin, drugs of abuse, theophylline, and warfarin, may alsobe monitored. In embodiments that monitor more than one analyte, theanalytes may be monitored at the same or different times.

The analyte monitoring system 100 includes an analyte sensor 101, a dataprocessing unit 102 connectable to the sensor 101, and a primaryreceiver unit 104. In some instances, the primary receiver unit 104 isconfigured to communicate with the data processing unit 102 via acommunication link 103. In certain embodiments, the primary receiverunit 104 may be further configured to transmit data to a data processingterminal 105 to evaluate or otherwise process or format data received bythe primary receiver unit 104. The data processing terminal 105 may beconfigured to receive data directly from the data processing unit 102via a communication link 107, which may optionally be configured forbi-directional communication. Further, the data processing unit 102 mayinclude a transmitter or a transceiver to transmit and/or receive datato and/or from the primary receiver unit 104 and/or the data processingterminal 105 and/or optionally a secondary receiver unit 106.

Also shown in FIG. 1 is an optional secondary receiver unit 106 which isoperatively coupled to the communication link 103 and configured toreceive data transmitted from the data processing unit 102. Thesecondary receiver unit 106 may be configured to communicate with theprimary receiver unit 104, as well as the data processing terminal 105.In certain embodiments, the secondary receiver unit 106 may beconfigured for bi-directional wireless communication with each of theprimary receiver unit 104 and the data processing terminal 105. Asdiscussed in further detail below, in some instances, the secondaryreceiver unit 106 may be a de-featured receiver as compared to theprimary receiver unit 104, for instance, the secondary receiver unit 106may include a limited or minimal number of functions and features ascompared with the primary receiver unit 104. As such, the secondaryreceiver unit 106 may include a smaller (in one or more, including all,dimensions), compact housing or embodied in a device including a wristwatch, arm band, PDA, mp3 player, cell phone, etc., for example.Alternatively, the secondary receiver unit 106 may be configured withthe same or substantially similar functions and features as the primaryreceiver unit 104. The secondary receiver unit 106 may include a dockingportion configured to mate with a docking cradle unit for placement by,e.g., the bedside for night time monitoring, and/or a bi-directionalcommunication device. A docking cradle may recharge a power supply.

Only one analyte sensor 101, data processing unit 102 and dataprocessing terminal 105 are shown in the embodiment of the analytemonitoring system 100 illustrated in FIG. 1. However, it will beappreciated by one of ordinary skill in the art that the analytemonitoring system 100 may include more than one sensor 101 and/or morethan one data processing unit 102, and/or more than one data processingterminal 105. Multiple sensors may be positioned in a user for analytemonitoring at the same or different times. In certain embodiments,analyte information obtained by a first sensor positioned in a user maybe employed as a comparison to analyte information obtained by a secondsensor. This may be useful to confirm or validate analyte informationobtained from one or both of the sensors. Such redundancy may be usefulif analyte information is contemplated in critical therapy-relateddecisions. In certain embodiments, a first sensor may be used tocalibrate a second sensor.

The analyte monitoring system 100 may be a continuous monitoring system,or semi-continuous, or a discrete monitoring system. In amulti-component environment, each component may be configured to beuniquely identified by one or more of the other components in the systemso that communication conflict may be readily resolved between thevarious components within the analyte monitoring system 100. Forexample, unique IDs, communication channels, and the like, may be used.

In certain embodiments, the sensor 101 is physically positioned in or onthe body of a user whose analyte level is being monitored. The sensor101 may be configured to at least periodically sample the analyte levelof the user and convert the sampled analyte level into a correspondingsignal for transmission by the data processing unit 102. The dataprocessing unit 102 is coupleable to the sensor 101 so that both devicesare positioned in or on the user's body, with at least a portion of theanalyte sensor 101 positioned transcutaneously. The data processing unitmay include a fixation element, such as an adhesive or the like, tosecure it to the user's body. A mount (not shown) attachable to the userand mateable with the data processing unit 102 may be used. For example,a mount may include an adhesive surface. The data processing unit 102performs data processing functions, where such functions may include,but are not limited to, filtering and encoding of data signals, each ofwhich corresponds to a sampled analyte level of the user, fortransmission to the primary receiver unit 104 via the communication link103. In some embodiments, the sensor 101 or the data processing unit 102or a combined sensor/data processing unit may be wholly implantableunder the skin surface of the user.

In certain embodiments, the primary receiver unit 104 may include ananalog interface section including an RF receiver and an antenna that isconfigured to communicate with the data processing unit 102 via thecommunication link 103, and a data processing section for processing thereceived data from the data processing unit 102 including data decoding,error detection and correction, data clock generation, data bitrecovery, etc., or any combination thereof.

In operation, the primary receiver unit 104 in certain embodiments isconfigured to synchronize with the data processing unit 102 to uniquelyidentify the data processing unit 102, based on, for example, anidentification information of the data processing unit 102, andthereafter, to periodically receive signals transmitted from the dataprocessing unit 102 associated with the monitored analyte levelsdetected by the sensor 101.

Referring again to FIG. 1, the data processing terminal 105 may includea personal computer, a portable computer including a laptop or ahandheld device (e.g., a personal digital assistant (PDA), a telephoneincluding a cellular phone (e.g., a multimedia and Internet-enabledmobile phone including an iPhone™, a Blackberry®, or similar phone), anmp3 player (e.g., an iPOD™, etc.), a pager, and the like), and/or a drugdelivery device (e.g., an infusion device), each of which may beconfigured for data communication with the receiver via a wired or awireless connection. Additionally, the data processing terminal 105 mayfurther be connected to a data network (not shown) for storing,retrieving, updating, and/or analyzing data corresponding to thedetected analyte level of the user.

The data processing terminal 105 may include a drug delivery device(e.g., an infusion device) such as an insulin infusion pump or the like,which may be configured to administer a drug (e.g., insulin) to theuser, and which may be configured to communicate with the primaryreceiver unit 104 for receiving, among others, the measured analytelevel. Alternatively, the primary receiver unit 104 may be configured tointegrate an infusion device therein so that the primary receiver unit104 is configured to administer an appropriate drug (e.g., insulin) tousers, for example, for administering and modifying basal profiles, aswell as for determining appropriate boluses for administration based on,among others, the detected analyte levels received from the dataprocessing unit 102. An infusion device may be an external device or aninternal device, such as a device wholly implantable in a user.

In certain embodiments, the data processing terminal 105, which mayinclude an infusion device, e.g., an insulin pump, may be configured toreceive the analyte signals from the data processing unit 102, and thus,incorporate the functions of the primary receiver unit 104 includingdata processing for managing the user's insulin therapy and analytemonitoring. In certain embodiments, the communication link 103, as wellas one or more of the other communication interfaces shown in FIG. 1,may use one or more wireless communication protocols, such as, but notlimited to: an RF communication protocol, an infrared communicationprotocol, a Bluetooth enabled communication protocol, an 802.11xwireless communication protocol, or an equivalent wireless communicationprotocol which would allow secure, wireless communication of severalunits (for example, per Health Insurance Portability and AccountabilityAct (HIPPA) requirements), while avoiding potential data collision andinterference.

FIG. 2 shows a block diagram of an embodiment of a data processing unit102 of the analyte monitoring system shown in FIG. 1. User input and/orinterface components may be included or a data processing unit may befree of user input and/or interface components. In certain embodiments,one or more application-specific integrated circuits (ASIC) may be usedto implement one or more functions or routines associated with theoperations of the data processing unit (and/or receiver unit) using forexample one or more state machines and buffers.

As can be seen in the embodiment of FIG. 2, the analyte sensor 101(FIG. 1) includes four contacts, three of which are electrodes: a workelectrode (W) 210, a reference electrode (R) 212, and a counterelectrode (C) 213, each operatively coupled to the analog interface 201of the data processing unit 102. This embodiment also shows an optionalguard contact (G) 211. Fewer or greater electrodes may be employed. Forexample, the counter and reference electrode functions may be served bya single counter/reference electrode. In some cases, there may be morethan one working electrode and/or reference electrode and/or counterelectrode, etc.

FIG. 3 is a block diagram of an embodiment of a receiver/monitor unitsuch as the primary receiver unit 104 of the analyte monitoring systemshown in FIG. 1. The primary receiver unit 104 includes one or more of:a test strip interface 301, an RF receiver 302, a user input 303, anoptional temperature detection section 304, and a clock 305, each ofwhich is operatively coupled to a processing and storage section 307.The primary receiver unit 104 also includes a power supply 306operatively coupled to a power conversion and monitoring section 308.Further, the power conversion and monitoring section 308 is also coupledto the processing and storage section 307. Moreover, also shown are areceiver serial communication section 309, and an output 310, eachoperatively coupled to the processing and storage section 307. Theprimary receiver unit 104 may include user input and/or interfacecomponents or may be free of user input and/or interface components.

In certain embodiments, the test strip interface 301 includes an analytetesting portion (e.g., a glucose level testing portion) to receive ablood (or other body fluid sample) analyte test or information relatedthereto. For example, the test strip interface 301 may include a teststrip port to receive a test strip (e.g., a glucose test strip). Thedevice may determine the analyte level of the test strip, and optionallydisplay (or otherwise notice) the analyte level on the output 310 of theprimary receiver unit 104. Any suitable test strip may be employed,e.g., test strips that only require a very small amount (e.g., 3microliters or less, e.g., 1 microliter or less, e.g., 0.5 microlitersor less, e.g., 0.1 microliters or less), of applied sample to the stripin order to obtain accurate glucose information. Embodiments of teststrips include, e.g., Freestyle® blood glucose test strips from AbbottDiabetes Care, Inc. (Alameda, Calif.). Glucose information obtained byan in vitro glucose testing device may be used for a variety ofpurposes, computations, etc. For example, the information may be used tocalibrate sensor 101, confirm results of sensor 101 to increase theconfidence thereof (e.g., in instances in which information obtained bysensor 101 is employed in therapy related decisions), etc.

In further embodiments, the data processing unit 102 and/or the primaryreceiver unit 104 and/or the secondary receiver unit 106, and/or thedata processing terminal/infusion device 105 may be configured toreceive the analyte value wirelessly over a communication link from, forexample, a blood glucose meter. In further embodiments, a usermanipulating or using the analyte monitoring system 100 (FIG. 1) maymanually input the analyte value using, for example, a user interface(for example, a keyboard, keypad, voice commands, and the like)incorporated in one or more of the data processing unit 102, the primaryreceiver unit 104, secondary receiver unit 106, or the data processingterminal/infusion device 105.

Additional detailed descriptions are provided in U.S. Pat. Nos.5,262,035; 5,264,104; 5,262,305; 5,320,715; 5,593,852; 6,175,752;6,650,471; 6,746, 582, and 7,811,231, each of which is incorporatedherein by reference in their entirety.

FIG. 4 schematically shows an embodiment of an analyte sensor 400 inaccordance with the embodiments of the present disclosure. This sensorembodiment includes electrodes 401, 402 and 403 on a base 404.Electrodes (and/or other features) may be applied or otherwise processedusing any suitable technology, e.g., chemical vapor deposition (CVD),physical vapor deposition, sputtering, reactive sputtering, printing,coating, ablating (e.g., laser ablation), painting, dip coating,etching, and the like. Materials include, but are not limited to, anyone or more of aluminum, carbon (including graphite), cobalt, copper,gallium, gold, indium, iridium, iron, lead, magnesium, mercury (as anamalgam), nickel, niobium, osmium, palladium, platinum, rhenium,rhodium, selenium, silicon (e.g., doped polycrystalline silicon),silver, tantalum, tin, titanium, tungsten, uranium, vanadium, zinc,zirconium, mixtures thereof, and alloys, oxides, or metallic compoundsof these elements.

The analyte sensor 400 may be wholly implantable in a user or may beconfigured so that only a portion is positioned within (internal) a userand another portion outside (external) a user. For example, the sensor400 may include a first portion positionable above a surface of the skin410, and a second portion positioned below the surface of the skin. Insuch embodiments, the external portion may include contacts (connectedto respective electrodes of the second portion by traces) to connect toanother device also external to the user such as a transmitter unit.While the embodiment of FIG. 4 shows three electrodes side-by-side onthe same surface of base 404, other configurations are contemplated,e.g., fewer or greater electrodes, some or all electrodes on differentsurfaces of the base or present on another base, some or all electrodesstacked together, electrodes of differing materials and dimensions, etc.

FIG. 5A shows a perspective view of an embodiment of an analyte sensor500 having a first portion (which in this embodiment may becharacterized as a major portion) positionable above a surface of theskin 510, and a second portion (which in this embodiment may becharacterized as a minor portion) that includes an insertion tip 530positionable below the surface of the skin, e.g., penetrating throughthe skin and into, e.g., the subcutaneous space 520, in contact with theuser's biofluid, such as interstitial fluid. Contact portions of aworking electrode 511, a reference electrode 512, and a counterelectrode 513 are positioned on the first portion of the sensor 500situated above the skin surface 510. A working electrode 501, areference electrode 502, and a counter electrode 503 are shown at thesecond portion of the sensor 500 and particularly at the insertion tip530. Traces may be provided from the electrodes at the tip to thecontact, as shown in FIG. 5A. It is to be understood that greater orfewer electrodes may be provided on a sensor. For example, a sensor mayinclude more than one working electrode and/or the counter and referenceelectrodes may be a single counter/reference electrode, etc.

FIG. 5B shows a cross sectional view of a portion of the sensor 500 ofFIG. 5A. The electrodes 501, 502 and 503, of the sensor 500 as well asthe substrate and the dielectric layers are provided in a layeredconfiguration or construction. For example, as shown in FIG. 5B, in oneembodiment, the sensor 500 (such as the analyte sensor unit 101 of FIG.1), includes a substrate layer 504, and a first conducting layer 501such as carbon, gold, etc., disposed on at least a portion of thesubstrate layer 504, and which may provide the working electrode. Alsoshown disposed on at least a portion of the first conducting layer 501is a sensing layer 508.

A first insulation layer 505, such as a first dielectric layer incertain embodiments, is disposed or layered on at least a portion of thefirst conducting layer 501, and further, a second conducting layer 509may be disposed or stacked on top of at least a portion of the firstinsulation layer (or dielectric layer) 505. As shown in FIG. 5B, thesecond conducting layer 509 may provide the reference electrode 502, asdescribed herein having an extended lifetime, which includes a layer ofredox polymer as described herein.

A second insulation layer 506, such as a second dielectric layer incertain embodiments, may be disposed or layered on at least a portion ofthe second conducting layer 509. Further, a third conducting layer 503may be disposed on at least a portion of the second insulation layer 506and may provide the counter electrode 503. Finally, a third insulationlayer 507 may be disposed or layered on at least a portion of the thirdconducting layer 503. In this manner, the sensor 500 may be layered suchthat at least a portion of each of the conducting layers is separated bya respective insulation layer (for example, a dielectric layer). Theembodiments of FIGS. 5A and 5B show the layers having different lengths.In certain instances, some or all of the layers may have the same ordifferent lengths and/or widths.

In certain embodiments, some or all of the electrodes 501, 502, 503 maybe provided on the same side of the substrate 504 in the layeredconstruction as described above, or alternatively, may be provided in aco-planar manner such that two or more electrodes may be positioned onthe same plane (e.g., side-by side (e.g., parallel) or angled relativeto each other) on the substrate 504. For example, co-planar electrodesmay include a suitable spacing therebetween and/or include a dielectricmaterial or insulation material disposed between the conductinglayers/electrodes. Furthermore, in certain embodiments, one or more ofthe electrodes 501, 502, 503 may be disposed on opposing sides of thesubstrate 504. In such embodiments, contact pads may be one the same ordifferent sides of the substrate. For example, an electrode may be on afirst side and its respective contact may be on a second side, e.g., atrace connecting the electrode and the contact may traverse through thesubstrate.

An embodiment of a sensing layer may be described as the area shownschematically in FIG. 5B as 508. The sensing layer may be described asthe active chemical area of the biosensor. The sensing layerformulation, which can include a glucose-transducing agent, may include,for example, among other constituents, a redox mediator, such as, forexample, a hydrogen peroxide or a transition metal complex, such as aruthenium-containing complex or an osmium-containing complex, and ananalyte-responsive enzyme, such as, for example, a glucose-responsiveenzyme (e.g., glucose oxidase, glucose dehydrogenase, etc.) orlactate-responsive enzyme (e.g., lactate oxidase). In certainembodiments, the sensing layer includes glucose oxidase. The sensinglayer may also include other optional components, such as, for example,a polymer and a bi-functional, short-chain, epoxide cross-linker, suchas polyethylene glycol (PEG).

In certain instances, the analyte-responsive enzyme is distributedthroughout the sensing layer. For example, the analyte-responsive enzymemay be distributed uniformly throughout the sensing layer, such that theconcentration of the analyte-responsive enzyme is substantially the samethroughout the sensing layer. In some cases, the sensing layer may havea homogeneous distribution of the analyte-responsive enzyme. In certainembodiments, the redox mediator is distributed throughout the sensinglayer. For example, the redox mediator may be distributed uniformlythroughout the sensing layer, such that the concentration of the redoxmediator is substantially the same throughout the sensing layer. In somecases, the sensing layer may have a homogeneous distribution of theredox mediator. In certain embodiments, both the analyte-responsiveenzyme and the redox mediator are distributed uniformly throughout thesensing layer, as described above.

As noted above, analyte sensors may include an analyte-responsive enzymeto provide a sensing component or sensing layer. Some analytes, such asoxygen, can be directly electrooxidized or electroreduced on a sensor,and more specifically at least on a working electrode of a sensor. Otheranalytes, such as glucose and lactate, require the presence of at leastone electron transfer agent and/or at least one catalyst to facilitatethe electrooxidation or electroreduction of the analyte. Catalysts mayalso be used for those analytes, such as oxygen, that can be directlyelectrooxidized or electroreduced on the working electrode. For theseanalytes, each working electrode includes a sensing layer (see forexample sensing layer 508 of FIG. 5B) proximate to or on a surface of aworking electrode. In many embodiments, a sensing layer is formed nearor on only a small portion of at least a working electrode.

The sensing layer includes one or more components constructed tofacilitate the electrochemical oxidation or reduction of the analyte.The sensing layer may include, for example, a catalyst to catalyze areaction of the analyte and produce a response at the working electrode,an electron transfer agent to transfer electrons between the analyte andthe working electrode (or other component), or both.

A variety of different sensing layer configurations may be used. Incertain embodiments, the sensing layer is deposited on the conductivematerial of a working electrode. The sensing layer may extend beyond theconductive material of the working electrode. In some cases, the sensinglayer may also extend over other electrodes, e.g., over the counterelectrode and/or reference electrode (or counter/reference is provided).

A sensing layer that is in direct contact with the working electrode maycontain an electron transfer agent to transfer electrons directly orindirectly between the analyte and the working electrode, and/or acatalyst to facilitate a reaction of the analyte. For example, aglucose, lactate, or oxygen electrode may be formed having a sensinglayer which contains a catalyst, including glucose oxidase, glucosedehydrogenase, lactate oxidase, or laccase, respectively, and anelectron transfer agent that facilitates the electrooxidation of theglucose, lactate, or oxygen, respectively.

In other embodiments the sensing layer is not deposited directly on theworking electrode. Instead, the sensing layer 508 may be spaced apartfrom the working electrode, and separated from the working electrode,e.g., by a separation layer. A separation layer may include one or moremembranes or films or a physical distance. In addition to separating theworking electrode from the sensing layer, the separation layer may alsoact as a mass transport limiting layer and/or an interferent eliminatinglayer and/or a biocompatible layer.

In certain embodiments which include more than one working electrode,one or more of the working electrodes may not have a correspondingsensing layer, or may have a sensing layer which does not contain one ormore components (e.g., an electron transfer agent and/or catalyst)needed to electrolyze the analyte. Thus, the signal at this workingelectrode may correspond to background signal which may be removed fromthe analyte signal obtained from one or more other working electrodesthat are associated with fully-functional sensing layers by, forexample, subtracting the signal.

In certain embodiments, the sensing layer includes one or more electrontransfer agents. Electron transfer agents that may be employed areelectroreducible and electrooxidizable ions or molecules having redoxpotentials that are a few hundred millivolts above or below the redoxpotential of the standard calomel electrode (SCE). The electron transferagent may be organic, organometallic, or inorganic. Examples of organicredox species are quinones and species that in their oxidized state havequinoid structures, such as Nile blue and indophenol. Examples oforganometallic redox species are metallocenes including ferrocene.Examples of inorganic redox species are hexacyanoferrate (III),ruthenium hexamine, etc. Additional examples include those described inU.S. Pat. Nos. 6,736,957, 7,501,053 and 7,754,093, the disclosures ofeach of which are incorporated herein by reference in their entirety.

In certain embodiments, electron transfer agents have structures orcharges which prevent or substantially reduce the diffusional loss ofthe electron transfer agent during the period of time that the sample isbeing analyzed. For example, electron transfer agents include but arenot limited to a redox species, e.g., bound to a polymer which can inturn be disposed on or near the working electrode. The bond between theredox species and the polymer may be covalent, coordinative, or ionic.Although any organic, organometallic or inorganic redox species may bebound to a polymer and used as an electron transfer agent, in certainembodiments the redox species is a transition metal compound or complex,e.g., osmium, ruthenium, iron, and cobalt compounds or complexes. Itwill be recognized that many redox species described for use with apolymeric component may also be used, without a polymeric component.

Embodiments of polymeric electron transfer agents may contain a redoxspecies covalently bound in a polymeric composition. An example of thistype of mediator is poly(vinylferrocene). Another type of electrontransfer agent contains an ionically-bound redox species. This type ofmediator may include a charged polymer coupled to an oppositely chargedredox species. Examples of this type of mediator include a negativelycharged polymer coupled to a positively charged redox species such as anosmium or ruthenium polypyridyl cation. Another example of anionically-bound mediator is a positively charged polymer includingquaternized poly(4-vinyl pyridine) or poly(1-vinyl imidazole) coupled toa negatively charged redox species such as ferricyanide or ferrocyanide.In other embodiments, electron transfer agents include a redox speciescoordinatively bound to a polymer. For example, the mediator may beformed by coordination of an osmium or cobalt 2,2′-bipyridyl complex topoly(1-vinyl imidazole) or poly(4-vinyl pyridine).

Suitable electron transfer agents are osmium transition metal complexeswith one or more ligands, each ligand having a nitrogen-containingheterocycle such as 2,2′-bipyridine, 1,10-phenanthroline, 1-methyl,2-pyridyl biimidazole, or derivatives thereof. The electron transferagents may also have one or more ligands covalently bound in a polymer,each ligand having at least one nitrogen-containing heterocycle, such aspyridine, imidazole, or derivatives thereof. One example of an electrontransfer agent includes (a) a polymer or copolymer having pyridine orimidazole functional groups and (b) osmium cations complexed with twoligands, each ligand containing 2,2′-bipyridine, 1,10-phenanthroline, orderivatives thereof, the two ligands not necessarily being the same.Some derivatives of 2,2′-bipyridine for complexation with the osmiumcation include but are not limited to 4,4′-dimethyl-2,2′-bipyridine andmono-, di-, and polyalkoxy-2,2′-bipyridines, including4,4′-dimethoxy-2,2′-bipyridine. Derivatives of 1,10-phenanthroline forcomplexation with the osmium cation include but are not limited to4,7-dimethyl-1,10-phenanthroline and mono, di-, andpolyalkoxy-1,10-phenanthrolines, such as4,7-dimethoxy-1,10-phenanthroline. Polymers for complexation with theosmium cation include but are not limited to polymers and copolymers ofpoly(1-vinyl imidazole) (referred to as “PVI”) and poly(4-vinylpyridine) (referred to as “PVP”). Suitable copolymer substituents ofpoly(1-vinyl imidazole) include acrylonitrile, acrylamide, andsubstituted or quaternized N-vinyl imidazole, e.g., electron transferagents with osmium complexed to a polymer or copolymer of poly(1-vinylimidazole).

Embodiments may employ electron transfer agents having a redox potentialranging from about −200 mV to about +200 mV versus the standard calomelelectrode (SCE). The sensing layer may also include a catalyst which iscapable of catalyzing a reaction of the analyte. The catalyst may also,in some embodiments, act as an electron transfer agent. One example of asuitable catalyst is an enzyme which catalyzes a reaction of theanalyte. For example, a catalyst, including a glucose oxidase, glucosedehydrogenase (e.g., pyrroloquinoline quinone (PQQ), dependent glucosedehydrogenase, flavine adenine dinucleotide (FAD) dependent glucosedehydrogenase, or nicotinamide adenine dinucleotide (NAD) dependentglucose dehydrogenase), may be used when the analyte of interest isglucose. A lactate oxidase or lactate dehydrogenase may be used when theanalyte of interest is lactate. Laccase may be used when the analyte ofinterest is oxygen or when oxygen is generated or consumed in responseto a reaction of the analyte.

In certain embodiments, a catalyst may be attached to a polymer, crosslinking the catalyst with another electron transfer agent, which, asdescribed above, may be polymeric. A second catalyst may also be used incertain embodiments. This second catalyst may be used to catalyze areaction of a product compound resulting from the catalyzed reaction ofthe analyte. The second catalyst may operate with an electron transferagent to electrolyze the product compound to generate a signal at theworking electrode. Alternatively, a second catalyst may be provided inan interferent-eliminating layer to catalyze reactions that removeinterferents.

In certain embodiments, the sensor operates at a low oxidizingpotential, e.g., a potential of about +40 mV vs. Ag/AgCl. This sensinglayer uses, for example, an osmium (Os)-based mediator constructed forlow potential operation. Accordingly, in certain embodiments the sensingelement is a redox active component that includes (1) osmium-basedmediator molecules that include (bidente) ligands, and (2) glucoseoxidase enzyme molecules. These two constituents are combined togetherin the sensing layer of the sensor.

A mass transport limiting layer (not shown), e.g., an analyte fluxmodulating layer, may be included with the sensor to act as adiffusion-limiting barrier to reduce the rate of mass transport of theanalyte, for example, glucose or lactate, into the region around theworking electrodes. The mass transport limiting layers are useful inlimiting the flux of an analyte to a working electrode in anelectrochemical sensor so that the sensor is linearly responsive over alarge range of analyte concentrations and is easily calibrated. Masstransport limiting layers may include polymers and may be biocompatible.A mass transport limiting layer may provide many functions, e.g.,biocompatibility and/or interferent-eliminating functions, etc.

In certain embodiments, a mass transport limiting layer is a membranecomposed of crosslinked polymers containing heterocyclic nitrogengroups, such as polymers of polyvinylpyridine and polyvinylimidazole.Embodiments also include membranes that are made of a polyurethane, orpolyether urethane, or chemically related material, or membranes thatare made of silicone, and the like.

A membrane may be formed by crosslinking in situ a polymer, modifiedwith a zwitterionic moiety, a non-pyridine copolymer component, andoptionally another moiety that is either hydrophilic or hydrophobic,and/or has other desirable properties, in an alcohol-buffer solution.The modified polymer may be made from a precursor polymer containingheterocyclic nitrogen groups. For example, a precursor polymer may bepolyvinylpyridine or polyvinylimidazole. Optionally, hydrophilic orhydrophobic modifiers may be used to “fine-tune” the permeability of theresulting membrane to an analyte of interest. Optional hydrophilicmodifiers, such as poly(ethylene glycol), hydroxyl or polyhydroxylmodifiers, may be used to enhance the biocompatibility of the polymer orthe resulting membrane.

A membrane may be formed in situ by applying an alcohol-buffer solutionof a crosslinker and a modified polymer over an enzyme-containingsensing layer and allowing the solution to cure for about one to twodays or other appropriate time period. The crosslinker-polymer solutionmay be applied to the sensing layer by placing a droplet or droplets ofthe membrane solution on the sensor, by dipping the sensor into themembrane solution, by spraying the membrane solution on the sensor, andthe like. Generally, the thickness of the membrane is controlled by theconcentration of the membrane solution, by the number of droplets of themembrane solution applied, by the number of times the sensor is dippedin the membrane solution, by the volume of membrane solution sprayed onthe sensor, or by any combination of these factors. A membrane appliedin this manner may have any combination of the following functions: (1)mass transport limitation, i.e., reduction of the flux of analyte thatcan reach the sensing layer, (2) biocompatibility enhancement, or (3)interferent reduction.

In some instances, the membrane may form one or more bonds with thesensing layer. By bonds is meant any type of an interaction betweenatoms or molecules that allows chemical compounds to form associationswith each other, such as, but not limited to, covalent bonds, ionicbonds, dipole-dipole interactions, hydrogen bonds, London dispersionforces, and the like. For example, in situ polymerization of themembrane can form crosslinks between the polymers of the membrane andthe polymers in the sensing layer. In certain embodiments, crosslinkingof the membrane to the sensing layer facilitates a reduction in theoccurrence of delamination of the membrane from the sensing layer.

In certain embodiments, the sensing system detects hydrogen peroxide toinfer glucose levels. For example, a hydrogen peroxide-detecting sensormay be constructed in which a sensing layer includes enzyme such asglucose oxides, glucose dehydrogenase, or the like, and is positionedproximate to the working electrode. The sensing layer may be covered byone or more layers, e.g., a membrane that is selectively permeable toglucose. Once the glucose passes through the membrane, it is oxidized bythe enzyme and reduced glucose oxidase can then be oxidized by reactingwith molecular oxygen to produce hydrogen peroxide.

Certain embodiments include a hydrogen peroxide-detecting sensorconstructed from a sensing layer prepared by combining together, forexample: (1) a redox mediator having a transition metal complexincluding an Os polypyridyl complex with oxidation potentials of about+200 mV vs. SCE, and (2) periodate oxidized horseradish peroxidase(HRP). Such a sensor functions in a reductive mode; the workingelectrode is controlled at a potential negative to that of the Oscomplex, resulting in mediated reduction of hydrogen peroxide throughthe HRP catalyst.

In another example, a potentiometric sensor can be constructed asfollows. A glucose-sensing layer is constructed by combining together(1) a redox mediator having a transition metal complex including Ospolypyridyl complexes with oxidation potentials from about −200 mV to+200 mV vs. SCE, and (2) glucose oxidase. This sensor can then be usedin a potentiometric mode, by exposing the sensor to a glucose containingsolution, under conditions of zero current flow, and allowing the ratioof reduced/oxidized Os to reach an equilibrium value. Thereduced/oxidized Os ratio varies in a reproducible way with the glucoseconcentration, and will cause the electrode's potential to vary in asimilar way.

The substrate may be formed using a variety of non-conducting materials,including, for example, polymeric or plastic materials and ceramicmaterials. Suitable materials for a particular sensor may be determined,at least in part, based on the desired use of the sensor and propertiesof the materials.

In some embodiments, the substrate is flexible. For example, if thesensor is configured for implantation into a user, then the sensor maybe made flexible (although rigid sensors may also be used forimplantable sensors) to reduce pain to the user and damage to the tissuecaused by the implantation of and/or the wearing of the sensor. Aflexible substrate often increases the user's comfort and allows a widerrange of activities. Suitable materials for a flexible substrateinclude, for example, non-conducting plastic or polymeric materials andother non-conducting, flexible, deformable materials. Examples of usefulplastic or polymeric materials include thermoplastics such aspolycarbonates, polyesters (e.g., Mylar™ and polyethylene terephthalate(PET)), polyvinyl chloride (PVC), polyurethanes, polyethers, polyamides,polyimides, or copolymers of these thermoplastics, such as PETG(glycol-modified polyethylene terephthalate).

In other embodiments, the sensors are made using a relatively rigidsubstrate to, for example, provide structural support against bending orbreaking. Examples of rigid materials that may be used as the substrateinclude poorly conducting ceramics, such as aluminum oxide and silicondioxide. An implantable sensor having a rigid substrate may have a sharppoint and/or a sharp edge to aid in implantation of a sensor without anadditional insertion device.

It will be appreciated that for many sensors and sensor applications,both rigid and flexible sensors will operate adequately. The flexibilityof the sensor may also be controlled and varied along a continuum bychanging, for example, the composition and/or thickness of thesubstrate.

In addition to considerations regarding flexibility, it is oftendesirable that implantable sensors should have a substrate which isphysiologically harmless, for example, a substrate approved by aregulatory agency or private institution for in vivo use.

The sensor may include optional features to facilitate insertion of animplantable sensor. For example, the sensor may be pointed at the tip toease insertion. In addition, the sensor may include a barb which assistsin anchoring the sensor within the tissue of the user during operationof the sensor. However, the barb is typically small enough so thatlittle damage is caused to the subcutaneous tissue when the sensor isremoved for replacement.

An implantable sensor may also, optionally, have an anticlotting agentdisposed on a portion of the substrate which is implanted into a user.This anticlotting agent may reduce or eliminate the clotting of blood orother body fluid around the sensor, particularly after insertion of thesensor. Blood clots may foul the sensor or irreproducibly reduce theamount of analyte which diffuses into the sensor. Examples of usefulanticlotting agents include heparin and tissue plasminogen activator(TPA), as well as other known anticlotting agents.

The anticlotting agent may be applied to at least a portion of that partof the sensor that is to be implanted. The anticlotting agent may beapplied, for example, by bath, spraying, brushing, or dipping, etc. Theanticlotting agent is allowed to dry on the sensor. The anticlottingagent may be immobilized on the surface of the sensor or it may beallowed to diffuse away from the sensor surface. The quantities ofanticlotting agent disposed on the sensor may be below the amountstypically used for treatment of medical conditions involving blood clotsand, therefore, have only a limited, localized effect.

Insertion Device

An insertion device can be used to subcutaneously insert the sensor intothe user. The insertion device is typically formed using structurallyrigid materials, such as metal or rigid plastic. Materials may includestainless steel and ABS (acrylonitrile-butadiene-styrene) plastic. Insome embodiments, the insertion device is pointed and/or sharp at thetip to facilitate penetration of the skin of the user. A sharp, thininsertion device may reduce pain felt by the user upon insertion of thesensor. In other embodiments, the tip of the insertion device has othershapes, including a blunt or flat shape. These embodiments may be usefulwhen the insertion device does not penetrate the skin but rather servesas a structural support for the sensor as the sensor is pushed into theskin.

Sensor Control Unit

The sensor control unit can be integrated in the sensor, part or all ofwhich is subcutaneously implanted or it can be configured to be placedon the skin of a user. The sensor control unit is optionally formed in ashape that is comfortable to the user and which may permit concealment,for example, under a user's clothing. The thigh, leg, upper arm,shoulder, or abdomen are convenient parts of the user's body forplacement of the sensor control unit to maintain concealment. However,the sensor control unit may be positioned on other portions of theuser's body. One embodiment of the sensor control unit has a thin, ovalshape to enhance concealment. However, other shapes and sizes may beused.

The particular profile, as well as the height, width, length, weight,and volume of the sensor control unit may vary and depends, at least inpart, on the components and associated functions included in the sensorcontrol unit. In general, the sensor control unit includes a housingtypically formed as a single integral unit that rests on the skin of theuser. The housing typically contains most or all of the electroniccomponents of the sensor control unit.

The housing of the sensor control unit may be formed using a variety ofmaterials, including, for example, plastic and polymeric materials, suchas rigid thermoplastics and engineering thermoplastics. Suitablematerials include, for example, polyvinyl chloride, polyethylene,polypropylene, polystyrene, ABS polymers, and copolymers thereof. Thehousing of the sensor control unit may be formed using a variety oftechniques including, for example, injection molding, compressionmolding, casting, and other molding methods. Hollow or recessed regionsmay be formed in the housing of the sensor control unit. The electroniccomponents of the sensor control unit and/or other items, including abattery or a speaker for an audible alarm, may be placed in the hollowor recessed areas.

The sensor control unit is typically attached to the skin of the user,for example, by adhering the sensor control unit directly to the skin ofthe user with an adhesive provided on at least a portion of the housingof the sensor control unit which contacts the skin or by suturing thesensor control unit to the skin through suture openings in the sensorcontrol unit.

When positioned on the skin of a user, the sensor and the electroniccomponents within the sensor control unit are coupled via conductivecontacts. The one or more working electrodes, counter electrode (orcounter/reference electrode), optional reference electrode, and optionaltemperature probe are attached to individual conductive contacts. Forexample, the conductive contacts are provided on the interior of thesensor control unit. Other embodiments of the sensor control unit havethe conductive contacts disposed on the exterior of the housing. Theplacement of the conductive contacts is such that they are in contactwith the contact pads on the sensor when the sensor is properlypositioned within the sensor control unit.

Sensor Control Unit Electronics

The sensor control unit also typically includes at least a portion ofthe electronic components that operate the sensor and the analytemonitoring device system. The electronic components of the sensorcontrol unit typically include a power supply for operating the sensorcontrol unit and the sensor, a sensor circuit for obtaining signals fromand operating the sensor, a measurement circuit that converts sensorsignals to a desired format, and a processing circuit that, at minimum,obtains signals from the sensor circuit and/or measurement circuit andprovides the signals to an optional transmitter. In some embodiments,the processing circuit may also partially or completely evaluate thesignals from the sensor and convey the resulting data to the optionaltransmitter and/or activate an optional alarm system if the analytelevel exceeds a threshold. The processing circuit often includes digitallogic circuitry.

The sensor control unit may optionally contain a transmitter fortransmitting the sensor signals or processed data from the processingcircuit to a receiver/display unit; a data storage unit for temporarilyor permanently storing data from the processing circuit; a temperatureprobe circuit for receiving signals from and operating a temperatureprobe; a reference voltage generator for providing a reference voltagefor comparison with sensor-generated signals; and/or a watchdog circuitthat monitors the operation of the electronic components in the sensorcontrol unit.

Moreover, the sensor control unit may also include digital and/or analogcomponents utilizing semiconductor devices, including transistors. Tooperate these semiconductor devices, the sensor control unit may includeother components including, for example, a bias control generator tocorrectly bias analog and digital semiconductor devices, an oscillatorto provide a clock signal, and a digital logic and timing component toprovide timing signals and logic operations for the digital componentsof the circuit.

As an example of the operation of these components, the sensor circuitand the optional temperature probe circuit provide raw signals from thesensor to the measurement circuit. The measurement circuit converts theraw signals to a desired format, using for example, a current-to-voltageconverter, current-to-frequency converter, and/or a binary counter orother indicator that produces a signal proportional to the absolutevalue of the raw signal. This may be used, for example, to convert theraw signal to a format that can be used by digital logic circuits. Theprocessing circuit may then, optionally, evaluate the data and providecommands to operate the electronics.

Calibration

Sensors may be configured to require no system calibration or no usercalibration. For example, a sensor may be factory calibrated and neednot require further calibrating. In certain embodiments, calibration maybe required, but may be done without user intervention, i.e., may beautomatic. In those embodiments in which calibration by the user isrequired, the calibration may be according to a predetermined scheduleor may be dynamic, i.e., the time for which may be determined by thesystem on a real-time basis according to various factors, including, butnot limited to, glucose concentration and/or temperature and/or rate ofchange of glucose, etc.

In addition to a transmitter, an optional receiver may be included inthe sensor control unit. In some cases, the transmitter is atransceiver, operating as both a transmitter and a receiver. Thereceiver may be used to receive calibration data for the sensor. Thecalibration data may be used by the processing circuit to correctsignals from the sensor. This calibration data may be transmitted by thereceiver/display unit or from some other source such as a control unitin a doctor's office. In addition, the optional receiver may be used toreceive a signal from the receiver/display units to direct thetransmitter, for example, to change frequencies or frequency bands, toactivate or deactivate the optional alarm system and/or to direct thetransmitter to transmit at a higher rate.

Calibration data may be obtained in a variety of ways. For instance, thecalibration data may be factory-determined calibration measurementswhich can be input into the sensor control unit using the receiver ormay alternatively be stored in a calibration data storage unit withinthe sensor control unit itself (in which case a receiver may not beneeded). The calibration data storage unit may be, for example, areadable or readable/writeable memory circuit.

Calibration may be accomplished using an in vitro test strip (or otherreference), e.g., a small sample test strip such as a test strip thatrequires less than about 1 microliter of sample (for example FreeStyle®blood glucose monitoring test strips from Abbott Diabetes Care, Alameda,Calif.). For example, test strips that require less than about 1nanoliter of sample may be used. In certain embodiments, a sensor may becalibrated using only one sample of body fluid per calibration event.For example, a user need only lance a body part one time to obtain asample for a calibration event (e.g., for a test strip), or may lancemore than one time within a short period of time if an insufficientvolume of sample is firstly obtained. Embodiments include obtaining andusing multiple samples of body fluid for a given calibration event,where glucose values of each sample are substantially similar. Dataobtained from a given calibration event may be used independently tocalibrate or combined with data obtained from previous calibrationevents, e.g., averaged including weighted averaged, etc., to calibrate.In certain embodiments, a system need only be calibrated once by a user,where recalibration of the system is not required.

Alternative or additional calibration data may be provided based ontests performed by a health care professional or by the user. Forexample, it is common for diabetic individuals to determine their ownblood glucose concentration using commercially available testing kits.The results of this test is input into the sensor control unit eitherdirectly, if an appropriate input device (e.g., a keypad, an opticalsignal receiver, or a port for connection to a keypad or computer) isincorporated in the sensor control unit, or indirectly by inputting thecalibration data into the receiver/display unit and transmitting thecalibration data to the sensor control unit.

Other methods of independently determining analyte levels may also beused to obtain calibration data. This type of calibration data maysupplant or supplement factory-determined calibration values.

In some embodiments of the invention, calibration data may be requiredat periodic intervals, for example, every eight hours, once a day, oronce a week, to confirm that accurate analyte levels are being reported.Calibration may also be required each time a new sensor is implanted orif the sensor exceeds a threshold minimum or maximum value or if therate of change in the sensor signal exceeds a threshold value. In somecases, it may be necessary to wait a period of time after theimplantation of the sensor before calibrating to allow the sensor toachieve equilibrium. In some embodiments, the sensor is calibrated onlyafter it has been inserted. In other embodiments, no calibration of thesensor is needed.

Analyte Monitoring Device

In some embodiments of the invention, the analyte monitoring deviceincludes a sensor control unit and a sensor. In these embodiments, theprocessing circuit of the sensor control unit is able to determine alevel of the analyte and activate an alarm system if the analyte levelexceeds a threshold value. The sensor control unit, in theseembodiments, has an alarm system and may also include a display, such asan LCD or LED display.

A threshold value is exceeded if the datapoint has a value that isbeyond the threshold value in a direction indicating a particularcondition. For example, a datapoint which correlates to a glucose levelof 200 mg/dL exceeds a threshold value for hyperglycemia of 180 mg/dL,because the datapoint indicates that the user has entered ahyperglycemic state. As another example, a datapoint which correlates toa glucose level of 65 mg/dL exceeds a threshold value for hypoglycemiaof 70 mg/dL because the datapoint indicates that the user ishypoglycemic as defined by the threshold value. However, a datapointwhich correlates to a glucose level of 75 mg/dL would not exceed thesame threshold value for hypoglycemia because the datapoint does notindicate that particular condition as defined by the chosen thresholdvalue.

An alarm may also be activated if the sensor readings indicate a valuethat is outside of (e.g., above or below) a measurement range of thesensor. For glucose, the physiologically relevant measurement range istypically 30-400 mg/dL, including 40-300 mg/dL and 50-250 mg/dL, ofglucose in the interstitial fluid.

The alarm system may also, or alternatively, be activated when the rateof change or acceleration of the rate of change in analyte levelincrease or decrease reaches or exceeds a threshold rate oracceleration. For example, in the case of a subcutaneous glucosemonitor, the alarm system may be activated if the rate of change inglucose concentration exceeds a threshold value which may indicate thata hyperglycemic or hypoglycemic condition is likely to occur. In somecases, the alarm system is activated if the acceleration of the rate ofchange in glucose concentration exceeds a threshold value which mayindicate that a hyperglycemic or hypoglycemic condition is likely tooccur.

A system may also include system alarms that notify a user of systeminformation such as battery condition, calibration, sensor dislodgment,sensor malfunction, etc. Alarms may be, for example, auditory and/orvisual. Other sensory-stimulating alarm systems may be used includingalarm systems which heat, cool, vibrate, or produce a mild electricalshock when activated.

Drug Delivery System

The subject invention also includes sensors used in sensor-based drugdelivery systems. The system may provide a drug to counteract the highor low level of the analyte in response to the signals from one or moresensors. Alternatively, the system may monitor the drug concentration toensure that the drug remains within a desired therapeutic range. Thedrug delivery system may include one or more (e.g., two or more)sensors, a processing unit such as a transmitter, a receiver/displayunit, and a drug administration system. In some cases, some or allcomponents may be integrated in a single unit. A sensor-based drugdelivery system may use data from the one or more sensors to providenecessary input for a control algorithm/mechanism to adjust theadministration of drugs, e.g., automatically or semi-automatically. Asan example, a glucose sensor may be used to control and adjust theadministration of insulin from an external or implanted insulin pump.

Each of the various references, presentations, publications, provisionaland/or non-provisional U.S. Patent Applications, U.S. Patents, non-U.S.Patent Applications, and/or non-U.S. Patents that have been identifiedherein, is incorporated herein by reference in its entirety.

Other embodiments and modifications within the scope of the presentdisclosure will be apparent to those skilled in the relevant art.Various modifications, processes, as well as numerous structures towhich the embodiments of the invention may be applicable will be readilyapparent to those of skill in the art to which the invention is directedupon review of the specification. Various aspects and features of theinvention may have been explained or described in relation tounderstandings, beliefs, theories, underlying assumptions, and/orworking or prophetic examples, although it will be understood that theinvention is not bound to any particular understanding, belief, theory,underlying assumption, and/or working or prophetic example. Althoughvarious aspects and features of the invention may have been describedlargely with respect to applications, or more specifically, medicalapplications, involving diabetic humans, it will be understood that suchaspects and features also relate to any of a variety of applicationsinvolving non-diabetic humans and any and all other animals. Further,although various aspects and features of the invention may have beendescribed largely with respect to applications involving partiallyimplanted sensors, such as transcutaneous or subcutaneous sensors, itwill be understood that such aspects and features also relate to any ofa variety of sensors that are suitable for use in connection with thebody of an animal or a human, such as those suitable for use as fullyimplanted in the body of an animal or a human. Finally, although thevarious aspects and features of the invention have been described withrespect to various embodiments and specific examples herein, all ofwhich may be made or carried out conventionally, it will be understoodthat the invention is entitled to protection within the full scope ofthe appended claims.

The following examples are put forth so as to provide those of ordinaryskill in the art with a complete disclosure and description of how tomake and use the embodiments of the invention, and are not intended tolimit the scope of what the inventors regard as their invention nor arethey intended to represent that the experiments below are all or theonly experiments performed. Efforts have been made to ensure accuracywith respect to numbers used (e.g., amounts, temperature, etc.) but someexperimental errors and deviations should be accounted for. Unlessindicated otherwise, parts are parts by weight, molecular weight isweight average molecular weight, temperature is in degrees Centigrade,and pressure is at or near atmospheric.

EXAMPLE 1 Sensors Having Membranes Incorporating aPoly(Styrene-Co-Maleic Anhydride) Polymer and a Poly(PropyleneGlycol)-Block-Poly(Ethylene Glycol)-Block-Poly(Propylene Glycol)Bis(2-Aminopropyl Ether) Crosslinker

Experiments were performed to test membrane formulations that included apoly(styrene-co-maleic anhydride) polymer (SMA polymer) and apoly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propyleneglycol) bis(2-aminopropyl ether) crosslinker (Jeffamine® ED-900crosslinker, Huntsman International LLC).

The membrane formulation was prepared and tested as follows.

Membrane Formulation:

For the SMA polymer solution, 167 mg SMA polymer was dissolved into 1 mL1,4-dioxane. For the Jeffamine® ED-900 solution, 230 mg Jeffamine®ED-900 was added into 1 mL 1,4-dioxane. The membrane solution wasprepared by mixing the SMA solution and the Jeffamine® ED-900 solution.

Testing Method:

The sensor was tested in 0.1 M PBS buffer containing 10 mM glucose witha temperature ranging from 27° C. to 42° C. The temperature wascontrolled by a circulated water system with a digital temperaturecontroller.

FIG. 6 shows graphs of the sensor signal over time at differenttemperatures for various membrane formulations that include a SMApolymer and a Jeffamine® ED-900 crosslinker. As demonstrated in FIG. 6,sensors that included a membrane with a SMA polymer and a Jeffamine®ED-900 crosslinker had a low temperature sensitivity, such that thesensor signal changed 1.5%/° C. or less over a range of temperatures(e.g., 27° C. to 42° C.). Data of temperature sensitivity for sensorsthat included a SMA polymer and a Jeffamine® ED-900 crosslinker is shownin Table 1 below.

TABLE 1 Temperature Effect on SMA/Jeffamine ® ED-900 Membrane Sensor/Current at Different Temperatures % Increase per ° C. under Air Membrane(nA, 5 mM glucose) 37° C. to 42° C. 42° C. to 32° C. 32° C. to 27° C.27° C. to 37° C. Type 37° C. 42° C. 32° C. 27° C. 37° C. individualaverage individual average individual average individual average 1%FADB2 9.155 8.911 9.521 10.132 9.521 −0.5% −0.2% 0.7% 0.4% 1.3% 0.8%−0.6% −0.3% (1 wk)1 1% FADB2 19.409 19.287 19.165 19.663 19.653 −0.1%−0.1% 0.5% 0.0% (1 wk)2 1% FADB2 9.521 9.399 10.01 10.498 9.888 −0.3%0.6% 1.0% −0.6% (1 wk)3 1% FADB2 14.038 14.16 14.404 14.771 14.648 −0.2%0.2% 0.5% −0.1% (1 wk)4 3% FADB2 8.301 7.935 8.423 8.911 8.301 −0.9%−0.7% 0.6% 0.8% 1.1% 0.9% −0.7% −0.7% (1 wk)1 3% FADB2 9.033 8.667 9.52110.01 9.155 −0.8% 0.9% 1.0% −0.9% (1 wk)2 3% FADB2 8.301 7.812 8.7899.155 8.301 −1.2% 1.2% 0.8% −1.0% (1 wk)3 3% FADB2 5.493 5.493 5.8596.104 5.859 0.0% 0.6% 0.8% −0.4% (1 wk)4 GOXB2 7.69 8.179 6.958 7.4468.545 1.2% 0.6% −1.6% −1.6% 1.4% 1.0% 1.4% 1.4% (3 dy)1 GOXB2 6.47 6.8365.737 6.104 7.08 1.1% −1.7% 1.2% 1.5% (3 dy)2 GOXB2 6.226 6.226 5.2495.493 6.226 0.0% −1.7% 0.9% 1.3% (3 dy)3 GOXB2 4.639 4.639 4.028 4.154.761 0.0% −1.4% 0.6% 1.4% (3 dy)4

In conclusion, the experiments above show that the addition of a SMApolymer and a Jeffamine® ED-900 crosslinker to a membrane formulationresulted in a membrane that had a low temperature sensitivity, such thatthe sensor signal changed 1.5%/° C. or less over the range oftemperatures tested.

EXAMPLE 2 Sensors Having Membranes Incorporating aPoly(4-Vinylpyridine)-Co-Polystyrene Polymer and anEpoxide-Polyehtyleneoxide-Polypropyleneoxide-Polyethyleneoxide-EpoxideCrosslinker

Experiments were performed to test membrane formulations that included apoly(4-vinylpyridine)-co-polystyrene polymer (PVPSty polymer) and anepoxide-polyehtyleneoxide-polypropyleneoxide-polyethyleneoxide-epoxidecrosslinker (epoxide-PEO-PPO-PEO-epoxide crosslinker).

The membrane formulation was prepared and tested as follows.

Membrane Formulation:

For the PVPSty polymer solution, 180 mg PVPSty polymer was dissolvedinto 1 mL ethanol. For the crosslinker solution, poly(ethylene glycol)(n) diglycidyl ether was mixed with Jeffamine® PD in a solution ofethanol and 20% 10 mM Hepes. The membrane solution was prepared bymixing 2 mL of the PVPSty solution and 0.5 mL of the crosslinkersolution, according to Table 2 below.

TABLE 2 PVPSty/Epoxide-PEO-PPO-PEO-epoxide Membrane Formulations CX-1Peg200 (318 mg/mL) + JFPD230 (115 mg · mL), MW 866, 216 mg/mL CX-2Peg200 (318 mg/mL) + JFPD430 (215 mg · mL), MW 1066, 266 mg/mL CX-3peg174 (174 mg/mL) + JFPD430 (215 mg/mL). MW 778, 194 mg/mL CX-4 peg174(174 mg/mL) + JFED900 (450 mg/mL). MW 1248, 312 mg/mL

Testing Method:

The sensor was tested in 0.1 M PBS buffer containing 10 mM glucose witha temperature ranging from 27° C. to 42° C. The temperature wascontrolled by a circulated water system with a digital temperaturecontroller.

FIG. 7 shows graphs of the sensor signal over time at differenttemperatures for various membrane formulations that include a PVPStypolymer and an epoxide-PEO-PPO-PEO-epoxide crosslinker. As demonstratedin FIG. 7, sensors that included a membrane with a PVPSty polymer and anepoxide-PEO-PPO-PEO-epoxide crosslinker had low temperature sensitivity,such that the sensor signal changed 3.5%/° C. or less over a range oftemperatures (e.g., 27° C. to 42° C.). Data of temperature sensitivityfor sensors that included a PVPSty polymer and anepoxide-PEO-PPO-PEO-epoxide crosslinker is shown in Table 3 below.

TABLE 3 Temperature Effect on PVPSty/Epoxide-PEO-PPO-PEO-epoxideMembrane Sensor/ Current at Different Temperatures % Increase per ° C.under Air Membrane (nA, 5 mM glucose) 37° C. to 42° C. 42° C. to 32° C.32° C. to 27° C. 27° C. to 37° C. Type 37° C. 42° C. 32° C. 27° C. 37°C. individual average individual average individual average individualaverage PVPSty- 30.4 34.5 26.4 22.2 30.6 2.6% 2.6% −2.7% −2.7% −3.4%−3.5% 3.3% 3.3% CX1 PVPSty- 29.9 34.1 25.9 21.7 30.2 2.6% −2.7% −3.4%3.3% CX1 PVPSty- 50.3 56.4 42.8 35.8 49.4 2.3% −2.7% −3.5% 3.3% CX1PVPSty- 30.3 34.5 26.4 22.1 30.5 2.7% −2.7% −3.5% 3.3% CX1 PVPSty- 34.437.7 30.4 26.2 34.1 1.8% 2.0% −2.1% −2.2% −2.9% −3.0% 2.6% 2.7% CX2PVPSty- 32.6 35.9 28.7 24.7 32.3 1.9% −2.2% −3.0% 2.8% CX2 PVPSty- 33.036.4 28.9 24.8 32.6 2.0% −2.3% −3.1% 2.8% CX2 PVPSty- 41.0 45.4 36.031.0 40.6 2.1% −2.3% −2.9% 2.7% CX2 PVPSty- 33.3 36.0 29.4 25.4 32.81.6% 1.6% −2.0% −2.0% −2.9% −2.9% 2.6% 2.7% CX3 PVPSty- 31.3 33.8 27.623.8 31.0 1.6% −2.0% −2.9% 2.7% CX3 PVPSty- 31.5 34.1 27.8 23.9 31.31.6% −2.0% −3.0% 2.7% CX3 PVPSty- 28.9 31.5 25.5 22.0 28.7 1.7% −2.1% —2.7% CX3 PVPSty- 28.8 34.7 25.6 21.4 30.3 3.8% 3.7% −3.0% −3.0% −3.6%−3.5% 3.5% 3.6% CX4 PVPSty- 33.4 39.9 29.7 24.8 35.2 3.6% −2.9% −3.5%3.6% CX4 PVPSty- 32.5 38.9 28.8 24.0 34.2 3.7% −3.0% −3.5% 3.6% CX4PVPSty- 31.3 37.4 27.7 23.2 32.8 3.6% −2.9% −3.5% 3.5% CX4

In conclusion, the experiments above show that the addition of a PVPStypolymer and an epoxide-PEO-PPO-PEO-epoxide crosslinker to a membraneformulation resulted in a membrane that had a low temperaturesensitivity, such that the sensor signal changed 3.5%/° C. or less overthe range of temperatures tested.

EXAMPLE 3 Sensors Having Membranes Incorporating aPoly(4-Vinylpyridine)-Co-Polystyrene Polymer, a Poly(Ethylene Glycol)(n) Diglycidyl Ether Crosslinker, and a Poly(Propylene Glycol) (n)Diglycidyl Ether Crosslinker

Experiments were performed to test membrane formulations that included apoly(4-vinylpyridine)-co-polystyrene polymer (PVPSty polymer), apoly(ethylene glycol) (n) diglycidyl ether crosslinker (Peg crosslinker)and a poly(propylene glycol) (n) diglycidyl ether crosslinker (Ppgcrosslinker).

The membrane formulation was prepared and tested as follows.

Membrane Formulation:

For the PVPSty polymer solution, 150 mg PVPSty polymer was dissolvedinto 1 mL ethanol. For the crosslinker solution, poly(ethylene glycol)(n) diglycidyl ether was mixed with poly(propylene glycol) (n)diglycidyl ether in a solution of ethanol and 20% 10 mM Hepes. Themembrane solution was prepared by mixing 2 mL of the PVPSty solution and0.4 mL of the crosslinker solution.

Testing Method:

The sensor was tested in 0.1 M PBS buffer containing 10 mM glucose witha temperature ranging from 27° C. to 42° C. The temperature wascontrolled by a circulated water system with a digital temperaturecontroller.

FIG. 8 shows graphs of the sensor signal over time at differenttemperatures for various membrane formulations that include a PVPStypolymer, a Peg crosslinker and a Ppg crosslinker. As demonstrated inFIG. 8, sensors that included a membrane with a PVPSty polymer, a Pegcrosslinker and a Ppg crosslinker had low temperature sensitivity, suchthat the sensor signal changed 4%/° C. or less over a range oftemperatures (e.g., 27° C. to 42° C.). Data of temperature sensitivityfor sensors that included a PVPSty polymer, a Peg crosslinker and a Ppgcrosslinker is shown in Table 4 below.

TABLE 4 Temperature Effect on PVPSty/Peg/Ppg Membrane Sensor/ Current atDifferent Temperatures % Increase per ° C. under Air Membrane (nA, 5 mMglucose) 37° C. to 42° C. 42° C. to 32° C. 32° C. to 27° C. 27° C. to37° C. Type 37° C. 42° C. 32° C. 27° C. 37° C. individual averageindividual average individual average individual average PVPSty 41.450.8 37.6 32.1 44.2 4.2% 4.1% −3.0% −3.0% −3.1% −3.1% 3.2% 3.3% 062810-4PVPSty 39.7 48.6 35.6 30.5 42.2 4.1% −3.0% −3.1% 3.3% 062810-4 PVPSty38.2 46.6 34.2 29.3 40.4 4.1% −3.1% −3.0% 3.3% 062810-4

In conclusion, the experiments above show that the addition of with aPVPSty polymer, a Peg crosslinker and a Ppg crosslinker to a membraneformulation resulted in a membrane that had a low temperaturesensitivity, such that the sensor signal changed 4%/° C. or less overthe range of temperatures tested.

EXAMPLE 4 Sensors Having Membranes Incorporating a Poly(EthyleneOxide-b-4-Vinyl Pyridine) Polymer and a Poly(Propylene Glycol) (n)Diglycidyl Ether Crosslinker

Experiments were performed to test membrane formulations that included apoly(ethylene oxide-b-4-vinyl pyridine) polymer (PEO-PVP polymer) and apoly(propylene glycol) (n) diglycidyl ether crosslinker (Ppgcrosslinker).

The membrane formulation was prepared and tested as follows.

Membrane Formulation:

For the PEO-PVP solution, 160 mg PEO-PVP polymer was dissolved into 1 mLethanol. For the crosslinker solution, poly(propylene glycol) (640)diglycidyl ether (150 mg) was added in 1 mL ethanol solution containing20% 10 mM Hepes. The membrane solution was prepared by mixing 21 mL ofthe PEO-PVP solution and 0.2 mL of the crosslinker solution.

Testing Method:

The sensor was tested in 0.1 M PBS buffer containing 10 mM glucose witha temperature ranging from 27° C. to 42° C. The temperature wascontrolled by a circulated water system with a digital temperaturecontroller.

FIG. 9 shows graphs of the sensor signal over time at differenttemperatures for various membrane formulations that include a PEO-PVPpolymer and a Ppg crosslinker. As demonstrated in FIG. 9, sensors thatincluded a membrane with a PEO-PVP polymer and a Ppg crosslinker had lowtemperature sensitivity, such that the sensor signal changed 2.5%/° C.or less over a range of temperatures (e.g., 27° C. to 42° C.). As acomparison, a control membrane formulation had a sensor signal thatchanged 5.5%/° C. over the same range of temperatures. Data oftemperature sensitivity for sensors that included a PEO-PVP polymer anda Ppg crosslinker is shown in Table 5 below.

TABLE 5 Temperature Effect on PEO-PVP/Ppg Membrane Sensor/ Current atDifferent Temperatures % Increase per ° C. under Air Membrane (nA, 5 mMglucose) 37° C. to 42° C. 42° C. to 32° C. 32° C. to 27° C. 27° C. to37° C. Type 37° C. 42° C. 32° C. 27° C. 37° C. individual averageindividual average individual average individual average control 1.8 2.31.5 1.1 1.8 4.8% 5.0% −4.5% −4.6% −5.6% −5.3% 5.2% 5.2% control 3.9 5.13.1 2.3 3.9 5.6% −5.1% −5.3% 5.4% control 4.9 6.2 3.9 3.1 4.9 5.0% −4.6%−4.8% 4.8% control 4.3 5.4 3.4 2.6 4.3 4.7% −4.4% −5.6% 5.2% PEO-PVP 8.29.0 7.3 6.5 8.2 2.0% 1.9% −2.1% −2.2% −2.4% −2.1% 2.4% 2.3% PEO-PVP 9.210.0 8.1 7.2 9.0 1.8% −2.1% −2.2% 2.3% PEO-PVP 9.6 10.6 8.4 7.7 9.4 1.9%−2.3% −1.8% 2.0% PEO-PVP 8.3 9.2 7.3 6.6 8.3 2.0% −2.2% −2.1% 2.3%PEO-LV 8.1 8.9 7.2 6.5 8.1 2.0% 2.1% −2.1% −2.1% −2.1% −2.1% 2.2% 2.1%PEO-LV 12.9 14.4 11.5 10.3 12.8 2.2% −2.2% −2.2% 2.3% PEO-LV 8.7 9.5 7.77.0 8.5 1.9% −2.1% −2.0% 2.1% PEO-LV 8.8 9.8 7.9 7.2 8.8 2.1% −2.1%−1.9% 2.0%

In conclusion, the experiments above show that the addition of with aPEO-PVP polymer and a Ppg crosslinker to a membrane formulation resultedin a membrane that had a low temperature sensitivity, such that thesensor signal changed 2.5%/° C. or less over the range of temperaturestested.

EXAMPLE 5 Sensors Having Membranes Incorporating a Poly(EthyleneOxide-b-4-Vinyl Pyridine) Polymer, aPoly(4-Vinylpyridine)-Co-Polystyrene Polymer, and a Poly(PropyleneGlycol) (n) Diglycidyl Ether Crosslinker

Experiments were performed to test membrane formulations that included apoly(ethylene oxide-b-4-vinyl pyridine) polymer (PEO-PVP polymer), apoly(4-vinylpyridine)-co-polystyrene (30%) polymer (PVP-Sty (30%)polymer), and a poly(propylene glycol) (n) diglycidyl ether crosslinker(Ppg crosslinker).

The membrane formulation was prepared and tested as follows.

Membrane Formulation:

For the PEO-PVP solution, 160 mg PEO-PVP polymer was dissolved into 1 mLethanol. For the PVP-Sty (30%) polymer solution, 150 mg PVPSty (30%)polymer was dissolved into 1 mL ethanol. For the crosslinker solution,poly(propylene glycol) (640) diglycidyl ether (150 mg) was added in 1 mLethanol solution containing 20% 10 mM Hepes. The membrane solution wasprepared by mixing 1 mL of the PEO-PVP solution, 1 mL of the PVPSty(30%) polymer solution, and 0.2 mL of the crosslinker solution.

Testing Method:

The sensor was tested in 0.1 M PBS buffer containing 10 mM glucose witha temperature ranging from 27° C. to 42° C. The temperature wascontrolled by a circulated water system with a digital temperaturecontroller.

FIG. 10 shows a graph of the sensor signal over time at differenttemperatures for a membrane formulation that included a PEO-PVP polymer,a PVP-Sty (30%) polymer, and a Ppg crosslinker. As demonstrated in FIG.10, sensors that included a membrane with a PEO-PVP polymer, a PVP-Sty(30%) polymer, and a Ppg crosslinker had a low temperature sensitivity,such that the sensor signal changed 2%/° C. or less over a range oftemperatures (e.g., 27° C. to 42° C.). As a comparison, a controlmembrane formulation had a sensor signal that changed 5.5%/° C. over thesame range of temperatures. Data of temperature sensitivity for sensorsthat included a PEO-PVP polymer, a PVP-Sty (30%) polymer, and a Ppgcrosslinker is shown in Table 6 below.

TABLE 6 Temperature Effect on PEO-PVP/PVP-Sty (30%)/Ppg Membrane Sensor/Current at Different Temperatures % Increase per ° C. under Air Membrane(nA, 5 mM glucose) 37° C. to 42° C. 42° C. to 32° C. 32° C. to 27° C.27° C. to 37° C. Type 37° C. 42° C. 32° C. 27° C. 37° C. individualaverage individual average individual average individual average control3.7 4.8 2.9 2.2 3.7 5.4% 5.2% −4.7% −4.9% −5.6% −5.6% 5.2% 5.4% control3.7 4.8 2.8 2.1 3.7 5.4% −5.1% −5.9% 5.8% control 4.3 5.4 3.3 2.4 4.24.7% −4.8% −5.8% 5.5% control 4.2 5.4 3.2 2.4 4.0 5.3% −5.1% −5.1% 5.1%PEO-PVP/ 7.0 7.4 6.3 5.7 7.0 1.4% 1.2% −1.6% −1.5% −2.0% −1.9% 1.9% 2.0%PVPSty (30%) PEO-PVP/ 7.6 8.1 6.6 6.2 7.6 1.3% −1.6% −1.9% 2.0% PVPSty(30%) PEO-PVP/ 5.1 5.4 4.6 4.3 5.1 0.9% −1.5% −1.6% 1.8% PVPSty (30%)PEO-PVP/ 6.2 6.6 5.7 5.1 6.3 1.1% −1.4% −2.2% 2.2% PVPSty (30%)

In conclusion, the experiments above show that the addition of a PEO-PVPpolymer, a PVP-Sty (30%) polymer, and a Ppg crosslinker to a membraneformulation resulted in a membrane that had a low temperaturesensitivity, such that the sensor signal changed 2%/° C. or less overthe range of temperatures tested.

1-67. (canceled)
 68. An analyte sensor comprising: a sensing layercomprising an analyte responsive enzyme; and a diffusion limitingpolymeric membrane disposed on the sensing layer, wherein the polymericmembrane comprises a poly(4-vinylpyridine)-co-polystyrene polymer, anethylene oxide substituent and a propylene oxide substituent, whereindiffusion of an analyte through the diffusion limiting membrane to thesensing layer does not change more than 5% per ° C. over a range ofphysiological temperatures.
 69. The analyte sensor of claim 68, whereinat least a portion of the analyte sensor is adapted to be subcutaneouslypositioned in a subject.
 70. The analyte sensor of claim 68, wherein thesensing layer comprises a glucose-responsive enzyme.
 71. The analytesensor of claim 70, wherein the glucose-responsive enzyme comprisesglucose oxidase.
 72. The analyte sensor of claim 68, wherein the sensinglayer further comprises a redox mediator.
 73. The analyte sensor ofclaim 72, wherein the redox mediator comprises a ruthenium-containingcomplex or an osmium-containing complex.
 74. The analyte sensor of claim72, wherein the redox mediator is bound to a polymer.
 75. The analytesensor of claim 68, wherein the analyte responsive enzyme is bound to apolymer.
 76. The analyte sensor of claim 68, wherein the analyte sensoris an in vivo glucose sensor.
 77. The analyte sensor of claim 68,wherein the polymer comprises a compound of the formula:

wherein x and y are each positive integers and the ratio of x to y is1:1.
 78. A method for monitoring a level of an analyte using an analytemonitoring system, the method comprising: inserting at least a portionof an analyte sensor according to claim 68 into skin of a patient;attaching an analyte sensor control unit to the skin of the patient andcoupling a plurality of conductive contacts of the analyte sensorcontrol unit to a plurality of contacts of the analyte sensor;collecting data, using the analyte sensor control unit, regarding alevel of an analyte from a signal generated by the analyte sensor; andtransmitting the collected data from the analyte sensor control unit toa receiver unit.
 79. The method of claim 78, wherein the analyte isglucose.
 80. The method of claim 78, wherein the collecting datacomprises generating signals from the analyte sensor and processing thesignals into data.
 81. The method of claim 78, wherein the data comprisethe signals from the analyte sensor.
 82. The method of claim 78, furthercomprising activating an alarm if the data indicate an alarm condition.83. The method of claim 78 further comprising administering a drug inresponse to the data.
 84. The method of claim 83, wherein the drug isinsulin.
 85. The method of claim 78, further comprising obtaining acalibration value from a calibration device to calibrate the data. 86.The method of claim 85, wherein the calibration device is coupled to adisplay unit.
 87. The method of claim 86, further comprisingtransmitting the calibration value from a transmitter in the displayunit to a receiver in the analyte sensor control unit.